Bis(phosphino)borates: A new family of monoanionic chelating phosphine ligands

Inorg. Chem. 2003, 42, 5055−5073

Bis(phosphino)borates: A New Family of Monoanionic Chelating

Phosphine Ligands

J. Christopher Thomas and Jonas C. Peters*

DiVision of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of

Chemical Synthesis, California Institute of Technology, Pasadena, California 91125

Received February 12, 2003

t

The reaction of dimethyldiaryltin reagents Me₂SnR (R ) Ph (1), p-MePh (2), m,m-Me₂Ph (3), p-BuPh (4), p-MeOPh

2

(5), p-CF Ph (6)) with BCl₃provided a high-yielding, simple preparative route to the corresponding diarylchloroboranes

3

t

R BCl (R ) Ph (10), p-MePh (11), m,m-Me₂Ph (12), p-BuPh (13), p-MeOPh (14), p-CF Ph (15)). In some cases,

2

3

the desired diarylchloroborane was not formed from an appropriate tin reagent Me₂SnR (R ) o-MeOPh (7),

2

o,o-(MeO)₂Ph (8), o-CF₃Ph (9)). The reaction of lithiated methyldiaryl- or methyldialkylphosphines with diaryl-

chloroboranes or dialkylchloroboranes is discussed. Specifically, several new monoanionic bis(phosphino)borates

t

are detailed: [Ph₂B(CH PPh₂)₂] (25); [(p-MePh)₂B(CH PPh₂)₂] (26); [(p-BuPh)₂B(CH PPh₂)₂] (27); [(p-MeOPh)₂B-

2

t

(CH PPh ) ] (28); [(p-CF Ph)₂B(CH PPh ) ] (29); [Cy₂B(CH PPh ) ] (30); [Ph B(CH P{p-BuPh}₂)₂] (31); [(p-MeOPh)₂B-

2

2 2

t

3

2

2 2

2

2 2

2

(CH P{p-BuPh}₂)₂] (32); [Ph₂B(CH P{p-CF Ph}₂)₂] (33); [Ph₂B(CH P(BH )(Me)₂)₂] (34); [Ph₂B(CH P(S)(Me)₂)₂] (35);

2

t

3

2

3

2

i

t

[Ph₂B(CH PPr₂)₂] (36); [Ph₂B(CH PBu₂)₂] (37); [(m,m-Me₂Ph)₂B(CH PBu₂)₂] (38). The chelation of diarylphosphine

2

derivatives 25−33 and 36 to platinum was examined by generation of a series of platinum dimethyl complexes.

The electronic effects of substituted bis(phosphino)borates on the carbonyl stretching frequency of neutral platinum

alkyl carbonyl complexes were studied by infrared spectroscopy. Substituents remote from the metal center (i.e. on

boron) have minimal effect on the electronic nature of the metal center, whereas substitution close to the metal

center (on phosphorus) has a greater effect on the electronic nature of the metal center.

I. Introduction

[Ph₂BP₂] ([Ph₂BP₂] ) [Ph₂B(CH₂PPh₂)₂]^-).^9,10The [Ph₂BP₂]

ligand is unique in that it preserves the essential properties

of a neutral bis(phosphine) chelate while also being anionic

in nature. Its chemical properties derive in part from the

Phosphines, perhaps more than any other single ligand

class, play a central role in both organic and inorganic

chemistry.¹It is striking to note that little attention has been

focused on anionic derivatives of these popular ligands.^2-8

To expand the range of anionic bis(phosphines), our group

recently introduced the anionic bis(phosphino)borate ligand

(3) (a) Ellermann, J.; Lietz, M. Z. Naturforsch., B 1980, 35, 64-67. (b)

Ellermann, J.; Lietz, M.; Geibel, K. Z. Anorg. Allg. Chem. 1982, 492,

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Chem. Soc., Dalton Trans. 1997, 3397-3401 and references therein.

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Commun. 1984, 1415-1416. (b) Karsch, H. H.; Appelt, A.; Ko¨hler,

F. H.; Mu¨ller, G. Organometallics 1985, 4, 231-238. (c) Karsch, H.

H.; Appelt, A.; Mu¨ller, G. Organometallics 1985, 4, 1624-1632. (d)

Karsch, H. H.; Appelt, A.; Riede, J.; Mu¨ller, G. Organometallics 1987,

6, 316-323.

* To whom correspondence should be addressed. E-mail: jpeters@

caltech.edu.

(1) (a) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.

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Published on Web 07/08/2003

Inorganic Chemistry, Vol. 42, No. 17, 2003 5055

Thomas and Peters

Scheme 1

carbanion delivery to haloborane reagents due to the pos-

sibility of kinetically problematic side reactions. While we

have yet to establish a truly general strategysphosphines

like those described herein required somewhat customized

methods of synthesisssignificant progress toward a simple

and generally effective approach to these bidentate systems

has been realized. Reaction solvents, reaction temperatures,

and the use of phosphine-protecting groups are among the

variables we consider in this study. Cation exchange

protocols are also emphasized as we have found, in separate

ongoing work, specific salt derivatives to be synthetically

most useful.

borate charge fastened into the alkyl chain of the ligand

backbone (Scheme 1).

Using an anionic borate unit to template di- and tripodal

donor ligands has been widely exploited since Trofimenko’s

early work.¹¹The (phosphino)borate ligands are distinct,

however, in that they introduce electronic and steric proper-

ties chemically divergent from previous borate-based sys-

tems. Moreover, despite the diverse areas to which they might

be applied, the chemistry of (phosphino)borate ligands is

essentially untapped. To make these ligand systems more

synthetically accessible, we have initiated studies to develop

reliable protocols for their synthesis. In this context, we now

provide detailed methods for the preparation of a series of

bis(phosphino)borate ligands comprising diverse electronic

and steric properties. We also make note of certain methods

that met with only limited success, realizing this type of

information will likely prove equally efficacious in the

continued development of this promising ligand family.

The general method we chose for preparing bis(phos-

phino)borate ligands relies on the delivery of a phosphi-

noalkyl carbanion to a borane electrophile. The advantage

of this strategy is its convergent approach: a host of borane

electrophiles and appropriate carbanions are synthetically

accessible. Also, the synthesis of borate-based ligands by

nucleophilic addition to borane precursors has precedence

in the literature, Riordan’s recent work being perhaps most

exemplary.¹²

In the results that follow, we discuss how each of the bis-

(phosphino)borates shown in Figure 1 was prepared, adhering

to the following format for presenting these data:

(i) methodology for generating diarylchloroborane elec-

trophiles of the form R₂BCl; (ii) methodology for generating

-

phosphine carbanions of the general form “R₂PCH₂”,

including potential synthetic advantages/disadvantages of

phosphine-protection protocols; (iii) generation of lithium

salts of the form [R₂B(CH₂PPh₂)₂][Li]; (iv) generation of

lithium salts of the form [Ph₂B(CH₂PR₂)₂][Li]; (v) methodol-

ogy for generating synthetically useful ammonium and

thallium salts of bis(phosphino)borates.

After the synthetic discussions, we include a consideration

of structural, spectroscopic, and electronic properties typical

of this emerging class of anionic phosphines. Specifically,

we provide infrared spectral data for a series of substituted

bis(phosphino)borate-platinum methyl carbonyl complexes

and examine the effects of various substitutions upon the

carbonyl stretching frequency.

II. Results and Discussion

Specific to (phosphino)borate ligands themselves was a

need to survey conditions compatible with clean phosphine

II.1. Boron Synthons. It was desirable to preferentially

study aryl-containing borates due to their typically enhanced

stability¹³compared to alkylborates. We therefore chose to

pursue the use of diarylhaloborane synthons. Arylhaloboranes

have been prepared previously by a variety of methods,^14-19

the most common of which rely on disproportionation of

haloboranes with aryl tin reagents. Since detailed descriptions

allowing for the direct and efficient synthesis of a variety of

diarylhaloboranes have not been previously described,

experimental procedures for the production of several R₂-

(7) (a) Qiao, S.; Hoic, D. A.; Fu, G. C. J. Am. Chem. Soc. 1996, 118,

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Chem. Commun. 1999, 2379-2380. (c) Shapiro, I. R.; Jenkins, D.

M.; Thomas, J. C.; Day, M. W.; Peters, J. C. Chem. Commun. 2001,

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Chem. Soc. 2002, 124, 11238-11239. (e) Jenkins, D. M.; Di Bilio,

A. J.; Allen, M. J.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.

2002, 124, 15336-15350. (f) Feldman, J. D.; Peters, J. C.; Tilley, T.

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J. C.; Tilley, T. D. Organometallics 2002, 21, 4065-4075. (h) Brown,

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17, 5492-5503.

5056 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

Figure 1. Representative drawings of the bis(phosphino)borates discussed.

Scheme 2

BCl reagents are provided herein. We acknowledge an

important lead from the laboratories of Chivers^18aand

Piers,^18bwho provided a reliable method for the preparation

of (C₆F₅)₂BCl from disproportionation of Me₂Sn(C₆F₅)₂and

BCl₃.

The first step in a two-step procedure required the

preparation of dimethyldiaryltin reagents, many of which

have been described in the literature previously.^20-27A wide

variety of dimethyldiaryltin reagents are readily synthesized

(19) (a) Eisch, J. J.; Shafii, B.; Odom, J. D.; Rheingold, A. L. J. Am. Chem.

Soc. 1990, 112, 1847-1853. (b) Pelter, A.; Singaram, B.; Warren,

L.; Wilson, J. W. Tetrahedron, 1993, 49, 2965-2978. (c) Pelter, A.;

Drake, R. Tetrahedron, 1994, 50, 13775-13800. (d) Pelter, A.; Drake,

R. Tetrahedron, 1994, 50, 13801-13828. (e) Pelter, A.; Drake, R.

Tetrahedron, 1994, 50, 13829-13846. (f) Gibson, V. C.; Redshaw,

C.; Clegg, W.; Elsegood, M. R. J. Polyhedron 1997, 16, 2637-2641.

(g) Ben, M. Z.; Chazalette, C.; Riviere-Baudet, M.; Riviere, P. Main

Group Met. Chem. 1999, 22, 405-412.

from dimethyltin dichloride and an appropriate aryl-Grignard

or aryllithium reagent. This procedure results in high isolated

yields of dimethyldiaryltin compounds Me₂SnR₂(R ) Ph

(1),^20-23p-MePh (2),^20,21,22,24m,m-(CH₃)₂Ph (3), p-^tBuPh (4),²⁵

p-MeOPh (5),^21,22,26p-CF₃Ph (6),²¹o-MeOPh (7),²²o,o-

(MeO)₂Ph (8),²⁷o-CF₃Ph (9)). In our hands, alkyl-, ether-,

and fluoro-substituted diaryltin reagents were successfully

prepared (Scheme 2).

(20) Kula, M.-R.; Amberger, E.; Mayer, K.-K. Chem. Ber. 1965, 98, 634-

637.

(21) Wilt, J. W.; Belmonte, F. G.; Zieske, P. A. J. Am. Chem. Soc. 1983,

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(22) Harada, G.; Yoshida, M.; Iyoda, M. Chem. Lett. 2000, 160-161.

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Soc. 1978, 100, 2779-2789. (b) Reich, H. J.; Holladay, J. E.; Mason,

J. D.; Sikorski, W. H. J. Am. Chem. Soc. 1995, 117, 12137-12150.

(24) Nagelberg, S. B.; Reinhold: C. E.; Willeford, B. R. Organometallics

1982, 1, 851-858.

In a second step, diarylchloroboranes were generated using

modified conditions of the Chivers/Piers methodology.¹⁸

A

(25) Apodaca, P.; Cervantes-Lee, F.; Pannell, K. H. Main Group Met. Chem.

2001, 24, 597-601.

(26) Rieke, R. D.; Tucker, I.; Milligan, S. N.; Wright, D. R.; Willeford, B.

R.; Radonovich, L. J.; Eyring, M. W. Organometallics 1982, 1, 938-

950.

(27) Wada, M.; Wakamori, H.; Hiraiwa, A.; Erabi, T. Bull. Chem. Soc.

Jpn. 1992, 65, 1389-1391.

heptane solution of BCl₃was introduced into a sealable

reaction vessel containing the dimethyldiaryltin reagent in

heptane. The sealed vessel was then heated in an oil bath

maintained at 100 °C for 24-72 h, depending on the tin

Inorganic Chemistry, Vol. 42, No. 17, 2003 5057

Thomas and Peters

Scheme 3

ously, most notably by the collective efforts of Karsch,

Schmidbaur, Peterson, and Schore.^29,30For example, Karsch

and Schmidbaur described the deprotonation of MeP^tBu₂and

PMe₃to prepare LiCH₂P^tBu₂(16) and Li(TMEDA)CH₂PMe₂

(20), respectively²⁹(TMEDA ) N,N,N′,N′-tetramethyleth-

ylenediamine). We have found that lithiation of MePⁱPr₂can

be achieved using conditions similar to those employed by

Karsch for the deprotonation of MeP^tBu₂. Thus, reaction of

t

neat MePⁱPr₂with desolvated BuLi at 60 °C for 24 h

provided white solids that, after washing with petroleum

ether, reacted cleanly as “ⁱPr₂PCH₂Li” (17) (eq 1). With

respect to diarylmethylphosphines, Peterson and Schore

demonstrated that deprotonation of MePPh₂was most

effectively accomplished using n-BuLi in the presence of

TMEDA, thereby producing Li(TMEDA)CH₂PPh₂(18).³⁰

By analogy, the alkyl-substituted diarylmethylphosphine

(p-^tBuPh)₂PMe deprotonated smoothly using similar condi-

tions to precipitate (p-^tBuPh)₂PCH₂Li(TMEDA) (19) as a

yellow solid (eq 2). As a cautionary note, we have found

that methyl-substituted arylphosphines, such as (2,4,6-Me₃-

Ph)₂PMe, can undergo competitive lithiation at the methyl

positions of the aryl rings. Additionally, attempts to depro-

tonate (p-CF₃Ph)₂PCH₃by this method led to extensive

decomposition.

reagent used. Our choice of incubating a heptane solution at

100 °C was chosen mainly for reasons of simplicity and

safety: previous methods employed hexanes at temperatures

exceeding the boiling point of the solvent in a closed system,

which we preferred to avoid. Additionally, BCl₃can be

purchased commercially as a heptane solution. The necessary

reaction time was dependent upon the electronic nature of

the aryl substituent: electron-poor aromatics required longer

reaction times to reach completion, whereas electron-rich

aromatics transferred very quickly. These observations are

consistent with an electrophilic attack by the boron center

on the aryl ring. Cooling of the vessel resulted in the

spontaneous crystallization of the dimethyltin dichloride

byproduct, which provided for easy recovery of this toxic

and somewhat expensive starting material. The recovered

Me₂SnCl₂was collected by filtration and then purified for

reuse via subsequent sublimation. Removal of the reaction

volatiles from the resultant solution under reduced pressure

at ambient temperature provided the desired diarylchloro-

borane reagents, typically in very pure form. Where neces-

sary, we have found that the isolated borane product can be

easily recrystallized from hydrocarbon solutions (e.g.,

petroleum ether, hexanes). Yields for these preparations when

carried out on 5-10 g scales were greater than 70% for all

but one case (Scheme 3). In addition to the parent borane

Ph₂BCl (10),^14,15we have successfully produced substituted

diarylchloroboranes using this methodology incorporating

either electron-donating ((p-MePh)₂BCl (11),^15,16(p-^tBuPh)₂BCl

(13), (p-MeOPh)₂BCl (14)^15,17) or electron-withdrawing

((p-CF₃Ph)₂BCl (15)) substituents at the para position.

Additionally, the meta-substituted borane (m,m-(CH₃)₂-

Ph)₂BCl (12) was prepared by the same method. Substitution

at the ortho position has proven more problematic. For

example, attempts to incorporate ortho-substituted meth-

oxyaryl groups resulted in cleavage at the aryl methyl ether

linkage, generating complex reaction mixtures (¹H and ¹¹B

NMR). Given the known ability for Lewis acidic haloboranes

to cleave ethers, particularly methyl aryl ethers,²⁸this was

not surprising. Attempts to place a sterically encumbering

CF₃group in an ortho position were also unsuccessful.

II.2. Phosphine Synthons. The lithiation of unprotected

dialkyl- and diarylmethylphosphines has been studied previ-

The deprotonation of tertiary phosphines protected by

BH₃^31,32and S³³has also been scrutinized due to its synthetic

utility with respect to preparing chiral phosphines, as was

first exemplified by Imamoto and co-workers.³²The advan-

tage of phosphine protection is that, owing to its increased

acidity, the methyl group undergoes deprotonation much

more rapidly. For example, the deprotonation of Ph₂(BH₃)-

PCH₃, (p-CF₃Ph)₂(BH₃)PCH₃, and Me₂(BH₃)PCH₃proceeded

cleanly at -78 °C in ethereal solution over the course of a

few hours, generating Ph₂(BH₃)P(CH₂Li) (21) (eq 3),³²(p-

CF₃Ph)₂(BH₃)P(CH₂Li) (22) (eq 3), and Me₂(BH₃)P(CH₂Li-

(TMEDA)) (23) in situ (eq 4).³¹Similarly, deprotonation of

sulfur-protected Me₂(S)PCH₃at -78 °C provided Me₂(S)-

P(CH₂Li(TMEDA)) (24) in situ (eq 4). For cases where the

reaction of unprotected phosphines with boranes led to

(28) For example: (a) Benton, F. L.; Dillon, T. E. J. Am. Chem. Soc. 1942,

64, 1128-1129. (b) Burwell, R. L., Jr. Chem. ReV. 1954, 54, 615-

685. (c) Gerrard, W.; Lappert, M. F. Chem. ReV. 1958, 58, 1081-

1111. (d) Guindon, Y.; Yoakim, C.; Morton, H. E. Tetrahedron Lett.

1983, 24, 2969-2972. (e) Guindon, Y.; Girard, Y.; Yoakim, C. J.

Org. Chem. 1987, 52, 1680-1686.

5058 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

undesirable results, the ease of synthesis of these reagents

makes them attractive carbanion synthons.

II.3.A. Bis(phosphino)borates: Substitution at Boron.

Preparation of the bis(phosphino)borate ligands themselves

was accomplished in a straightforward manner by condensa-

tion of the lithio phosphine reagents with borane electro-

philes. To examine the generality of this approach, we first

canvassed the condensation of Ph₂PCH₂Li(TMEDA) (18)

with several different borane electrophiles. The reaction

between 18 and a diarylchloroborane in general proceeded

cleanly under a single reaction condition (Et₂O/toluene, -78

°C to room temperature). Only the fluorine-containing borane

15 showed any propensity to form undesired side products

under these conditions. Thus, preparation of bis(phosphino)-

borate ligands from functionalized diarylchloroboranes was

achieved by reaction of 2 equiv of 18 with 10, 11, and 13-

15, to generate [Ph₂B(CH₂PPh₂)₂][Li(TMEDA)_x] (25[Li]),⁹

[(p-MePh)₂B(CH₂PPh₂)₂][Li(TMEDA)_x] (26[Li]), [(p-^t-

BuPh)₂B(CH₂PPh₂)₂][Li(TMEDA)_x] (27[Li]), [(p-MeOPh)₂B-

(CH₂PPh₂)₂][Li(TMEDA)_x] (28[Li]), and [(p-CF₃Ph)₂B(CH₂-

PPh₂)₂][Li(TMEDA)_x] (29[Li]). In general, ³¹P NMR spectra

of the crude reaction mixtures established successful syn-

thesis and yield as well as reaction times. Most of the

Li(TMEDA) salts of the bis(phosphino)borates described

above evinced some solubility in a range of solvents,

including toluene, THF, CH₃CN, acetone, and ethanol. The

ether- and perfluoroalkyl-substituted derivatives 28 and 29

showed greater solubility (Et₂O, benzene). We note that all

of the bis(phosphino)borate ligands, including those described

below, are incompatible with the halogenated solvents CHCl₃

and CH₂Cl₂, undergoing rapid decomposition upon dissolu-

tion. Degradation in chlorinated solvents is not generally

problematic when the ligands are coordinated to transition

metal ions.

The commercially available synthon bis(cyclohexyl)-

chloroborane also provided successful entry into bis(phos-

phino)borate chemistry. Using the same methodology as for

[Ph₂BP₂], the analogous ligand [Cy₂B(CH₂PPh₂)₂][Li-

(TMEDA)_x] (30[Li]) was prepared. Preparation proceeded

cleanly, and the product was purified for use by washing

with petroleum ether. Further purification to remove any

remaining lithium chloride salts was achieved by crystal-

lization of 30[Li] from diethyl ether or toluene at -30 °C.

An attempt to incorporate another commercially available

borane reagent, Mes₂BF (Mes ) 2,4,6-Me₃Ph), proved

unsuccessful under conditions analogous to those used for

other boranes. The absence of reactivity under the conditions

Figure 2. Protected alkylbis(phosphino)borates.

examined is most likely due to the high degree of steric

hindrance at boron. While not thoroughly explored as yet,

more forcing conditions may prove successful for reaction

between Mes₂BF and Ph₂PCH₂Li(TMEDA) (18).

II.3.B. Bis(phosphino)borates: Substitution at Phos-

phorus. We next examined the reactivity of several R₂PCH₂-

Li reagents with borane electrophiles. Substituted aryl groups

can provide different electronic and steric environments

around a coordinated metal, in addition to variable solubility.

Two substituted methyldiarylphosphines were examined.

Reaction of 2 equiv of (p-^tBuPh)₂PCH₂Li(TMEDA) (19) with

either Ph₂BCl (10) or (p-MeOPh)₂BCl (14) under the

previously described conditions resulted in the generation

of [Ph₂B(CH₂P{p-^tBuPh}₂)₂][Li(TMEDA)_x] (31[Li]) and [(p-

MeOPh)₂B(CH₂P{p-^tBuPh}₂)₂][Li(TMEDA)_x] (32[Li]). We

also inspected the fluorine-containing synthon (p-CF₃-

Ph)₂PMe to generate bis(phosphino)borates. Since direct

lithiation of this phosphine was unsuccessful (vide supra), a

borane protection strategy was used. Generation of (p-CF₃-

Ph)₂(BH₃)PCH₃proceeded readily by addition of BH₃‚SMe₂.

Subsequent deprotonation (s-BuLi at -78 °C over 2 h)

followed by addition of Ph₂BCl provided the protected bis-

(phosphino)borate [Ph₂B{CH₂P(p-CF₃Ph)₂(BH₃)}₂][Li] (33‚

BH₃[Li]). Removal of the BH₃protecting groups was

accomplished by dissolution of 33‚BH₃in neat morpholine

at 60 °C for 12 h, providing 33[Li].

We also desired to extend our ability to substitute bis-

(phosphino)borate ligands by examining alkyl substituents

on phosphorus. To this end, we attempted to prepare the

simple methyl-substituted derivative [Ph₂B(CH₂PMe₂)₂].

Direct reaction of Me₂PCH₂Li(TMEDA) (20) with diphen-

ylchloroborane resulted in the formation of multiple products.

We presume this to be due to the competitive formation of

Lewis acid r base complexes that prevent nucleophilic

carbanion addition to the borane center.³⁴In accord with this

suggestion, the BH₃-protected carbanion, Me₂P(BH₃)CH₂-

Li(TMEDA) (23), reacted productively with Ph₂BCl (10) to

produce the desired borate [Ph₂B(CH₂P(BH₃)Me₂)₂]-

[Li(TMEDA)_x] (34) (Figure 2). Likewise, the in situ-

generated sulfur-protected reagent, Me₂P(S)CH₂Li (24),

reacted cleanly to afford [Ph₂B(CH₂P(S)Me₂)₂] (35) (Figure

2), an intriguing S-donor ligand in its own right.

(29) Karsch, H. H.; Schmidbaur, H. Z. Naturforsch. 1977, 32B, 762-767.

(30) (a) Peterson, D. J. J. Organomet. Chem. 1967, 8, 199. (b) Schore, N.

E.; Benner, L. S.; Labelle, B. E. Inorg. Chem. 1981, 20, 3200-3208.

(31) Schmidbaur, H. J. Organomet. Chem. 1981, 200, 287-306 and

references therein.

(32) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K. J. Am.

Chem. Soc. 1990, 112, 5244-5252.

(33) (a) Mathey, F. Tetrahedron 1974, 30, 3127-3137. (b) Mathey, F.;

Mercier, F. Tetrahedron Lett. 1979, 3081-3084. (c) Chen, C. H.;

Brighty, K. E. Tetrahedron Lett. 1980, 4421-4424. (d) Karsch, H.

H. Chem. Ber. 1982, 115, 818-822. (e) Corey, E. J.; Chen, Z.;

Tanoury, G. J. J. Am. Chem. Soc. 1993, 115, 11000-11001. (f) Muci,

A. R.; Campos, K. R.; Evans, D. A. J. Am. Chem. Soc. 1995, 117,

9075-9076.

Attempts to deprotect either the borane- or sulfur-protected

borates 34 and 35 have met with very limited success. For

example, to deprotect 34, a host of literature protocols for

(34) Karsch et al. have reported similar results using aluminum electrophiles.

See ref 4.

Inorganic Chemistry, Vol. 42, No. 17, 2003 5059

Thomas and Peters

deprotecting phosphine-boranes were tried. These included

heating the borane-protected borate in neat morpholine or

diethylamine,³²refluxing in toluene with an excess of

DABCO,³⁵reaction with HBF₄‚Me₂O,³⁶and attempting to

reduce it by Pd/C in ethanol.³⁷Additionally, heating 34 in

toluene with an excess of PMe₃, or even in neat ⁿBu₃P, was

examined. None of these methods were successful in that,

even for those methods that did evince some degree of

productive deprotection, isolation of synthetically viable

sources of the deprotected [Ph₂B(CH₂PMe₂)₂]^-could not be

accomplished. Likewise, either decomposition or no reaction

at all resulted for the attempted deprotection of 35 using

previously reported routes, such as Cl₃SiSiCl₃,³⁸MeOTf/

(Me₂N)₃P,³⁹MeOTf/RS^-,⁴⁰lithium aluminum hydride in

(phosphino)borates 36-38 to be appreciably less stable than

their aryl substituted counterparts. This was true with respect

to oxidation, hydrolysis, and also thermal decomposition.

II.4. Generation of Ammonium and Thallium Salts.

Under many conditions, the lithium and Li(TMEDA) salts

of bis(phosphino)borates prove to be excellent reagents

themselves; however, we have also found ammonium and

thallium reagents to be effective for the metalation of

transition metal precursors.^8c-e,h,9,10The reaction products of

such reactions are often highly dependent on the nature of

the countercation. We therefore explored the salt exchange

of several bis(phosphino)borates. Although we have chosen

to specifically describe the formation of ASN (ASN )

5-azoniaspiro[4.4]nonane) salts⁴⁴here owing to the crystal-

linity they impart on coordinated metal salts, similar protocols

are also effective for commercially available ammonium

salts, such as tetrabutylammonium bromide and tetraethyl-

ammonium chloride.⁴⁵

n

refluxing dioxane,⁴¹and Bu₃P.⁴²Also, attempts to reduce

35 with sodium naphthalide⁴³or magnesium anthracene were

equally unsuccessful. In general, we therefore note that direct

deprotection of the alkyl-substituted (phosphino)borate ligands

was far more chemically challenging than deprotection of

the corresponding aryl-substituted deriVatiVes. This is pre-

sumably due to a very high degree of thermodynamic

stability in the anionic (alkylphosphino)borate-to-borane

adduct complexes.

Because the simple methyl-substituted phosphines proved

reluctant to release their protection groups, we examined

bulkier alkyl carbanions with the hope that steric crowding

would disfavor formation of the Lewis acid r base adducts

and therefore not require phosphine protection. We were

i

gratified to find that Pr₂PCH₂Li (17) reacted with Ph₂BCl

(10) in a mixture of THF and Et₂O to produce the target

ligand [Ph₂B(CH₂PⁱPr₂)₂][Li(THF)₂] (36[Li]) in good yield

(essentially quantitative by ³¹P NMR). In similar fashion, 2

equiv of ^tBu₂PCH₂Li (16) reacted with Ph₂BCl (10) in Et₂O/

THF to form [Ph₂B(CH₂P^tBu₂)₂][Li(OEt₂)] (37[Li]). Once

again, the reaction proceeded very cleanly according to the

crude ³¹P NMR spectrum. Both 36[Li] and 37[Li] could be

crystallized from Et₂O at -30 °C. The related ligand [(m,m-

Me₂Ph)₂B(CH₂P^tBu₂)₂][Li(OEt₂)] (38[Li]), was also prepared

by room-temperature reaction of 2 equiv of ^tBu₂PCH₂Li (16)

with (m,m-Me₂Ph)₂BCl (12) in Et₂O/THF and crystallized

from Et₂O at -30 °C. High isolated crystalline yields of

alkyl-substituted bis(phosphino)borates have proven difficult

due to their increased solubility; however, spectra of the

crude reactions typically show the presence of a single major

product. In general, we haVe found the alkyl-substituted

Salt exchange was straightforward for alkyl-substituted aryl

borates 25-27 and 31. The poor solubility of the ammonium

bis(phosphino)borates in EtOH provided a general means for

removing (TMEDA)Li halide. The generation of tetraalkyl-

ammonium salts by direct salt metathesis using ammonium

halides in ethanol succeeded for 25[Li], 26[Li], 27[Li], and

31[Li], providing [Ph₂B(CH₂PPh₂)₂][ASN] (25[ASN]),⁹[(p-

MePh)₂B(CH₂PPh₂)₂][ASN] (26[ASN]), [(p-^tBuPh)₂B(CH₂-

PPh₂)₂][ASN] (27[ASN]), and [Ph₂B(CH₂P{p-^tBuPh}₂)₂]-

[ASN] (31[ASN]).

In contrast, cation exchange for the MeO- and CF₃-

substituted arylborates 28[Li] and 29[Li] was problematic

due to their respective solubilities. The preparation of [(p-

CF₃Ph)₂B(CH₂PPh₂)₂][ASN] (29[ASN]) by dissolution in

acetone with (ASN)Br followed by filtration, concentration,

and crystallizing at -35 °C did prove successful. The

synthesis of [(p-MeOPh)₂B(CH₂PPh₂)₂][ASN] (28[ASN]),

however, was much more challenging. The most favorable

results were obtained by generating the BH₃-protected

phosphine ligand by deprotonation of MePPh₂‚BH₃followed

by reaction with 14 to form [(p-MeOPh)₂B{CH₂P(Ph)₂-

(BH₃)}₂][Li(solvent)_x] (28‚BH₃[Li]) and then carrying out

salt metathesis in ethanol with (ASN)Br. The resulting

product, [(p-MeOPh)₂B{CH₂P(Ph)₂(BH₃)}₂][ASN] (28‚BH₃-

[ASN]), can be converted through borane deprotection to

(35) Brisset, H.; Gourdel, Y.; Pellon, P.; Le Corre, M. Tetrahedron Lett.

1993, 4523-4526.

(36) McKinstery, L.; Livinghouse, T. Tetrahedron 1995, 51, 7655-7666.

(37) Couturier, M.; Tucker, J. L.; Andresen, B. M.; Dube´, P.; Negri, J. T.

Org. Lett. 2001, 3, 465-467.

(38) (a) Naumann, K.; Zon, G.; Mislow, K. J. Am. Chem. Soc. 1969, 91,

7012-7023. (b) Zon, G.; DeBruin, K. E.; Naumann, K.; Mislow, K.

J. Am. Chem. Soc. 1969, 91, 7023-7027.

(39) Omelan´czuk, J.; Mikołajczyk, M. Tetrahedron Lett. 1984, 25, 2493-

2496.

(40) Omelan´czuk, J.; Mikołajczyk, M. J. Am. Chem. Soc. 1979, 101, 7292-

7295.

(41) (a) King, R. B.; Cloyd, Jr., J. C. J. Am. Chem. Soc. 1975, 97, 46-52.

(b) King, R. B.; Cloyd, Jr., J. C. J. Am. Chem. Soc. 1975, 97, 53-60.

(42) Gorla, F.; Venanzi, L. M.; Albinati, A. Organometallics 1994, 13,

43-54.

(44) Blicke, F. F.; Hotelling, E. B. J. Am. Chem. Soc. 1954, 76, 5099-

5103.

(45) For reference, we have included the [ⁿBu₄N] and [Et₄N] salts of

[Ph₂B(CH₂PPh₂)₂] in the experimental data.

(43) Olah, G. A.; Hehemann, D. J. Org. Chem. 1977, 42, 2190.

5060 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

the desired compound, 28[ASN], albeit with a reduction in

yield of the ligand. The use of a phosphine-borane adduct

precursor for the cation metathesis step may prove ultimately

beneficial for certain ligand derivatives: deprotonation of

various (aryl)₂(BH₃)PCH₃complexes occurs much more

readily than those of the corresponding phosphines, and the

resulting bis(phosphino)borate products are likely to be more

stable to air and moisture than their unprotected counterparts.

Similarly, phosphine-sulfides may also prove to be effective

reagents for preparation of bis(phosphino)borates. The

limitation for either borane- or sulfide-protected phosphines

is the possibility for their successful and high-yielding

deprotection.

Figure 3. A 50% displacement ellipsoid representation of [Ph₂B(CH₂-

PPh₂)₂][Li(TMEDA)₂] (25[Li]). Hydrogen atoms and the [Li(TMEDA)₂]

cation are omitted for clarity.

To examine the ability to form thallium salts of phenyl-

substituted bis(phosphino)borates, we prepared the compound

[Ph₂B(CH₂PPh₂)₂][Tl] (25[Tl]). Salt exchange occurred upon

combination of EtOH solutions of 25[Li] and TlPF₆. Over

30 min, off-white solids precipitated which were collected

and further purified by crystallization from THF. For this

salt exchange, it was not necessary that 25[Li] be rigorously

pure from additional LiCl. It remains in the EtOH solution,

as does any excess TlPF₆. Purified 25[Tl] displayed several

noteworthy properties. First, its NMR spectra were best

obtained in THF-d₈, as the product displays poor solubility

in other hydrocarbon or polar solvents, including benzene,

toluene, acetone, and acetonitrile. Second, although ¹H NMR

spectra of 25[Tl] were obtained that showed no remarkable

features, the ³¹P NMR signals were difficult to detect at

ambient temperature. This contrasts the ³¹P NMR spectrum

obtained of crude 25[Tl], which shows a broad singlet at 57

ppm. Examination of a THF-d₈solution of 25[Tl] demon-

strated that a temperature-dependent exchange phenomenon

was operative. Thus, at low temperature (-65 °C), the ³¹P

NMR spectrum showed a doublet centered at 52.5 ppm, with

a typical, large phosphorus-thallium coupling constant of

4166 Hz. Upon warming, the peaks coalesced between -20

and 0 °C. Further warming to 55 °C provided a broad singlet

at 57.9 ppm.

A thallium adduct of 38 was also synthesized. Salt

exchange was effected by stirring a toluene solution of 38[Li]

with thallium nitrate. (A similar method works equally well

for related 37[Li].) The thallium-phosphorus coupling

constant observed for 38[Tl] in benzene is exceptionally large

(6334 Hz) but is reduced upon dissolution in a more polar

solvent such as THF (5933 Hz). This change in the P-Tl

coupling constant likely reflects the greater ability of THF

solvent to coordinate to the thallium cation relative to

benzene solvent or an aromatic ring of a bis(phosphino)-

borate molecule (vide infra).

provided ³¹P NMR chemical shifts within a narrow range

(-6 to -12 ppm), providing a second diagnostic handle.

Because of the large number of NMR-active nuclei, some

specific resonances were distinctly altered: ipso carbons

attached to boron were observed as broad quartets in ¹³C-

{¹H} NMR spectra (155 to 175 ppm), methylene carbons

and protons between boron and phosphorus were significantly

broadened, and uncoordinated bis(phosphino)borates often

evinced coupling between phosphorus and boron (²J_P-B).

To provide structural data for this new ligand class, X-ray

diffraction studies were carried out on select derivatives. The

previously described bis(phosphino)borate [Ph₂BP₂] (25) was

crystallized as its Li(TMEDA)₂salt, and a representation of

its structural data is shown in Figure 3. As can be seen from

the figure, even in the absence of an alkali metal cation, the

ligand adopts a confirmation well-poised to accept a metal

ion.

The related thallium salt of 25 was also studied by X-ray

crystallography to further probe the intriguing exchange

phenomenon eluded to above. A structural determination of

crystalline 25[Tl] revealed a coordination polymer structure

where the thallium cation joins two bis(phosphino)borate

molecules by coordinating to one phosphorus atom and one

borate aryl ring from each molecule (Figure 4). On the basis

of the structural determination, the ³¹P NMR data is best

explained by a highly labile binding of thallium by phos-

phorus. Note that the thallium atom is four-coordinate and

is best described by two Tl-P interactions and two η⁶-aryl

interactions. The Tl-C_aryldistances range from 3.239(3) to

3.403(4) Å (see Supporting Information for greater detail).

This contrasts the coordination observed for a related bis-

(phosphino)borate-thallium complex (vide infra).

Crystals of alkyl-substituted bis(phosphino)borates 36[Li]

and 37[Li] were also studied by X-ray diffraction. Structural

representations are shown in Figures 5 and 6. Common to

both structures is the coordination of the lithium cation by

the bis(phosphino)borate. Interestingly, the two structures

provide different coordination numbers for the lithium

cations. The sterically encumbering tert-butyl groups of

37[Li] restrict the coordination environment around lithium

to 3-coordinate, allowing only a single diethyl ether molecule

to coordinate. In contrast, the structure of the lithium ion in

36[Li] is more typically 4-coordinate, with two THF

molecules coordinated to the lithium cation.

II.5. Structural and Spectroscopic Data for Bis(phos-

phino)borates. In general, bis(phosphino)borates contain

relatively unremarkable spectral properties. Several features

of note come from the wide variety of NMR active nuclei

(¹H, ¹³C, ³¹P, ¹¹B). In all cases, ¹¹B and ³¹P NMR were useful

for analyzing the contents of crude reaction mixtures. The

desired tetraalkyl-substituted borates have distinctive ¹¹B

NMR chemical shifts and sharp resonances which allow for

easy identification. All of the aryl-substituted phosphines

Inorganic Chemistry, Vol. 42, No. 17, 2003 5061

Thomas and Peters

Figure 6. A 50% displacement ellipsoid representation of [Ph₂B(CH₂P-

^tBu₂)₂][Li(OEt₂)] (37[Li]). Hydrogen atoms and disordered positions are

omitted for clarity. Selected interatomic distances (Å) and angles (deg):

P-Li, 2.485(4); Li-O, 1.926(8); B-Li, 4.092(8); P-Li-O, 121.31(14);

P-Li-P, 99.5(2).

Figure 4. (A) A 50% displacement ellipsoid representation of {[Ph₂B(CH₂-

PPh₂)₂][Tl]}_n(25[Tl]), showing two anionic bis(phosphino)borate units and

one interconnecting thallium. Hydrogen atoms are omitted for clarity. (B)

Expanded view of the thallium coordination sphere. Selected interatomic

distances (Å) and angles (deg): P1-Tl, 3.0283(9); P2-Tl, 3.0231(9); Tl-

C_aryl(av), 3.311(5).

Figure 7. (A) A 50% displacement ellipsoid representation of [(m,m-

(CH₃)₂Ph)₂B(CH₂P^tBu₂)₂][Tl] (38[Tl]). Hydrogen atoms and second mol-

ecule of the asymmetric unit are omitted for clarity. Selected interatomic

distances (Å) and angles (deg): P1-Tl1, 2.9919(12); P2-Tl1, 2.9426(11);

B1-Tl1, 4.786(5); P1-Tl1-P2, 78.75(3). (B) Intermolecular interactions

within the asymmetric unit, emphasizing the thallium coordination sphere.

Selected interatomic distances (Å) and angles (deg): P3-Tl2, 2.9788(12);

P4-Tl2, 2.9406(11); C11-Tl2, 3.388(4); C12-Tl2, 3.353(4).

Figure 5. A 50% displacement ellipsoid representation of [Ph₂B(CH₂-

PⁱPr₂)₂][Li(THF)₂] (36[Li]). Hydrogen atoms are omitted for clarity. Selected

interatomic distances (Å) and angles (deg): Li-P1, 2.608(3); Li-P2,

2.596(3); Li-O1, 1.962(3); Li-O2, 1.928(3); Li-B, 4.197(3); P1-Li-

P2, 91.07(9); O1-Li-O2, 104.93(14); P1-Li-O1, 116.77(13); P2-Li-

O2, 107.46(13); P1-Li-O2, 112.56(13); P2-Li-O1, 123.68(13).

II.6. Discussion of Electronic Properties Characteristic

of Bis(phosphino)borate Ligands. Our remaining objective

is to consider the electronic properties of the bis(phosphino)-

borate ligands that have been described herein. To do this,

we report the spectroscopic characterization of a series of

neutral, platinum(II) carbonyl complexes supported by these

ligands. A key issue we consider is whether a zwitterionic

description is most appropriate for neutral complexes sup-

ported by these new ligands.

The impetus to describe neutral complexes supported by

(phosphino)borate ligands as zwitterionic derives from the

lack of simple resonance contributors that can efficiently

delocalize the anionic borate charge to the coordinated metal

center. From an electron-counting perspective, the zwitter-

ionic formulation suggests that metal complexes supported

by bis(phosphino)borates be regarded as cationic complexes

chelated by an L₂, 4-electron-donor ligand.⁴⁶This electronic

An X-ray diffraction experiment carried out on crystals

of 38[Tl] grown from benzene showed a structure distinct

from 25[Tl] in that the thallium cation is coordinated by two

phosphines and garners additional electron density from the

aryl ring of an adjacent arylborate group (Figure 7). The

thallium center in 38[Tl] is best described as three-coordinate,

with two phosphine donors and a single η²-aryl interaction

(see Supporting Information for greater detail). The nomi-

nally 3-coordinate structures determined for both the lithium

and thallium adducts of the sterically crowded [Ph₂B(CH₂-

P^tBu₂)₂] ligand provide a promising lead for developing low-

coordinate transition metal chemistry based upon this

particular ligand type.

5062 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

Table 1. ³¹P NMR Signals and Carbonyl Stretching Frequencies for Bis(phosphino)borate-Platinum Methyl Carbonyl Complexes 49-58

c

complex

³¹P NMR, δ (¹J_Pt-P, Hz)

ν

_CO(cm^-1

)

[Ph₂B(CH₂PPh₂)₂]Pt(Me)(CO) (49)

20.15 (3053), 15.53 (1637)^a

20.33 (3062), 15.92 (1645)^a

20.00 (3044), 15.32 (1639)^b

19.89 (3053), 15.43 (1640)^b

18.75 (3061), 14.24 (1631)^b

20.42 (3037), 16.23 (1646)^a

17.48 (3030), 12.68 (1641)^b

17.65 (3034), 12.93 (1642)^a

20.85 (3090), 16.84 (1616)^a

40.28 (1666), 30.81 (2942)^b

2094

2097

2092

2091

2105

2079

[(p-MePh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (50)

[(p-^tBuPh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (51)

[(p-MeOPh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (52)

[(p-CF₃Ph)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (53)

[Cy₂B(CH₂PPh₂)₂]Pt(Me)(CO) (54)

[Ph₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)(CO) (55)

[(p-MeOPh)₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)(CO) (56)

[Ph₂B(CH₂P{p-CF₃Ph}₂)₂]Pt(Me)(CO) (57)

[Ph₂B(CH₂PⁱPr₂)₂]Pt(Me)(CO) (58)

^aCDCl₃. ^bCD₂Cl₂. ^cCH₂Cl₂.

stretching frequencies recorded for the neutral systems are

invariably much lower in energy than their corresponding

cationic systems. This fact intimates that (phosphino)borate

ligands are appreciably more electron-releasing than their

neutral ligand congeners. Data consistent with this summary

has now been examined for several model carbonyl systems

featuring different metals (Fe, Ru, Rh, Co, Pd, Pt) in a range

of stereochemical environments (trigonal pyramidal, square

pyramidal, square planar, and octahedral).^{8d,9b,10,47,48}

Given these data, it is surprising how well the overall

reactivity of the zwitterionic systems we have thus far

examined compares with their isostructural but cationic

cousins. Clearly, the anionic field of the borate charge is

experienced by the coordinated metal center in these

complexes but does not significantly detract from their ability

to mediate transformations typical of their more electrophilic,

cationic cousins.^9,10,47

Figure 8. Selected resonance contributors for (A) bis(phosphino)borates

and (B) bis(pyrazolyl)borates.

Of obvious concern is to consider the degree to which

infrared CO data are actually reflective of the electronic

distribution for these systems. We therefore collected infrared

data for the series of platinum complexes shown in Table 1

to tune electronic effects at a position remote from the

coordinated metal center and to determine whether the CO

stretching frequency would be sensitive to such tuning.

As for the preparation of [Ph₂BP₂]Pt(Me)(CO),^9bthe

dimethyl complexes were prepared by reaction of the bis-

(phosphine) ligand with (COD)PtMe₂, which in most cases

led to rapid and quantitative displacement of cyclooctadiene

(eq 7). The sterically encumbered ligand 37 (and its relative

38) was the only phosphine ligand that failed to displace

cyclooctadiene, even at elevated temperatures (80 °C).

Subsequent protonation of each dimethyl complex by an

ammonium salt (e.g., [HNEt₃][BPh₄]) in THF, followed by

introduction of an atmosphere of CO, cleanly generated the

desired neutral methyl carbonyl complexes [R₂B(CH₂PR′₂)₂]-

Pt(Me)(CO) (49-58, eq 8). Their IR spectra were recorded

in CH₂Cl₂solution (KBr cell) to provide the relevant CO

stretching frequencies (Table 1).

description is distinct from the delocalized description

typically offered for the related families of bis- and tris-

(pyrazolyl)borates.^11,46In the (pyrazolyl)borates, the borate

charge is presumed to be more uniformly distributed due to

important resonance contributors that fully delocalize the

borate charge. In the extreme, electron-counting schemes

designate bis(pyrazolyl)borates as LX-type, 3-electron-

donors, whereas bis(phosphino)borates can be classified as

4-electron, L₂-donor ligands coordinated to a formal cation.

To underscore and clarify this distinction, Figure 8 provides

several conceivable resonance forms for a hypothetical bis-

(phosphino)borate complex and several reasonable resonance

forms of the bis(pyrazolyl)borate system. Some structures

shown for the bis(phosphino)borate system emphasize an

ylide resonance contributor of these anions.

To comparatively probe electronic factors, we have

reported infrared data for neutral metal carbonyl complexes

supported by both (phosphino)- and (amino)borate ligands

and have compared these data to that of their isostructural

but formally cationic carbonyl analogues.^8d,9b,10,47The results

of these model studies are collectively summarized as

follows: despite the utility in the zwitterionic descriptor, CO

(46) (a) Green, M. L. H. J. Organomet. Chem. 1995, 500, 127-148. (b)

Crabtree, R. H. The Organometallic Chemistry of the Transition

Metals, 3rd ed.; John Wiley & Sons: New York, 2001; pp 31-34,

137.

(47) (a) Betley, T. A.; Peters, J. C. Inorg. Chem. 2002, 41, 6541-6543.

(b) Betley, T. A.; Peters, J. C. Angew. Chem., Int. Ed. 2003, 2385-

2389.

Inorganic Chemistry, Vol. 42, No. 17, 2003 5063

Thomas and Peters

As can be seen from the infrared data, variation of the

borate backbone by systematic para substitution on the

phenyl ring (e.g., -H, -CH₃, -^tBu, -OMe, -CF₃) has

rather little effect on the observed CO stretching frequencies.

Indeed, aside from the CF₃-substituted derivative, each of

the complexes shown provides an indistinguishable CO

stretching frequency of 2094 cm^-1. The difference in the

observed CO stretching frequency (∆ν_CO) between the MeO-

substituted and the CF₃-substituted derivatives is only 3 cm^-1.

This modest difference is striking in view of the large

difference in the CO stretching frequency (∆ν_CO) +24

cm^-1) measured between [Ph₂BP₂]Pt(Me)(CO) and its cat-

ionic counterpart [(Ph₂SiP₂)PtMe(CO)][BAr₄] (Ph₂SiP₂)

Ph₂Si(CH₂PPh₂)₂).^9bReplacement of the diaryl backbone by

a dialkyl backbone, as in the Cy₂B derivative, provides a

slightly more electron-releasing ligand. Perhaps expectedly,

more pronounced effects are observed by para substitution

at the arylphosphine donor positions. For example, the

electron-releasing para-tert-butyl-substituted derivative, 55,

has a ν_COat 2091 cm^-1, whereas the para-CF₃-substituted

derivative, 57, provides a ν_COat 2105 cm^-1, a 14 cm^-1

difference. The sensitivity of the CO stretching frequency

as a function of variation at the borate backbone in these

neutral complexes appears to be quite small (2-3 cm^-1) or

negligible. Variation at the phosphine donors has an ap-

preciably more pronounced effect. This outcome is consistent

with describing the borate unit as electronically insulated,

at least to some degree.

releasing character of a ligand. This dilemma of variable

polarization is avoided within a contiguous series of neutral

carbonyl complexes, such as those provided in Table 1. The

relative ν_COvalues recorded are more reflective of relative

“electron-releasing” character.

It is interesting to also note that the subtle differences

recorded for the IR data are also manifest in the respective

³¹P NMR shifts of the methyl carbonyl complexes. The

magnitude of the separation (between 4 and 5 ppm) between

the two signals remains fairly constant across the series, and

complexes with identical ν_COstretches exhibit nearly identical

³¹P NMR shifts, as well as NMR coupling constants.

From the spectroscopic data collected in Table 1, it is

reasonable to conclude that electronic variation by substitu-

tion at the arylborate unit of the bis(phosphino)borate ligands

has only a small, if any, electronic impact on the electron-

releasing character of the phosphine ligands. This view is

consistent with the zwitterionic resonance contributor for

neutral complexes derived from these ligands. Data reported

elsewhere, however, that compare the electrophilicity of these

zwitterions with their isostructural cations strongly suggest

that the zwitterions are appreciably more electron-rich.^9b,10,47

Considering both sets of data collectively, one can therefore

anticipate a step change in the relative electrophilicity of a

metal center on moving from a neutral to a formally cationic

system, regardless of whether the neutral system is formally

zwitterionic. In other words, the anionic (phosphino)borates

are clearly more electron-releasing than their neutral

counterpartssa chemically plausible outcome. However, the

degree to which the borate charge is actually disseminated

throughout the complex is perhaps overly emphasized by

infrared data that compare a cationic to a neutral system.

To reconcile this conclusion with the comparative infrared

data for the neutral versus cationic platinum carbonyl

complexes, it needs to be underscored that the absolute

magnitude in ∆ν_COmeasured between a zwitterionic complex

(e.g., [Ph₂BP₂]Pt(Me)(CO)) and a cationic complex (e.g.,

[(Ph₂SiP₂)Pt(Me)(CO)][BAr₄]) is somewhat misleading for

the following reason. In cationic late metal carbonyls, where

π-back-bonding is relatively weak, strong polarization of the

CO σ-bond by the cationic complex is anticipated.⁴⁹This

raises the energy of the force constant F_COdramatically, and

in extreme cases, polarization can dominate the observed F_CO.

In this context, cationic complexes such as [(Ph₂SiP₂)PtMe]⁺

are expected to have characteristically high force constants

F_COdue to a strong polarization effect. This effect will be

much reduced for CO coordinated to a neutral [Ph₂BP₂]PtMe

fragment, regardless of whether its charge is distributed

asymmetrically due to a zwitterionic resonance contributor.

We therefore caution that the absolute magnitude of ∆ν_CO

is not so reliable a gauge of relative back-bonding ability

between complexes that are formally cationic and complexes

that are formally neutral. Large differences in polarization

between isostructural cationic and neutral complexes likely

compete with the electronic contributors of σ donation,

π-back-bonding, and/or π-acceptor character that we typically

rely upon to correlate measured ∆ν_COvalues to the electron-

Conclusion

This paper has outlined a general synthetic protocol used

to prepare a new family of bis(phosphino)borate ligands. The

methods described provide a path to construct ligands of

these types with varying substitution patterns at both the

borate and phosphine donor positions. These same protocols

are proving efficacious in the synthesis of tris(phosphino)-

borate ligands.⁵⁰While the protocols are in general effective,

we have uncovered problematic scenarios that can arise. Most

noteworthy is the synthesis of less sterically encumbered

derivatives, as in our attempted synthesis of the anion

[Ph₂B(CH₂PMe₂)₂]. Clean carbanion delivery to the borane

electrophile proved problematic in this case. While this

problem can be circumvented by an initial phosphine

protection step, deprotection protocols that afford the desired

ligand are nontrivial. The high σ-donor strength of the

[Ph₂B(CH₂PMe₂)₂] anion is an excellent example that il-

lustrates when deprotection becomes extremely problematic.

For arylphosphine donors, protection/deprotection protocols

are far more straightforward and, in certain cases, are

required, as for the case of ligand 33. Fortunately, alkyl-

substituted ligands, such as [Ph₂B(CH₂PⁱPr₂)₂] and

[Ph₂B(CH₂P^tBu₂)₂], are readily prepared without protection.

(48) Peters, J. C.; et al. Unpublished results.

(49) (a) Goldman, A. S.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1996,

118, 12159-12166. (b) Caulton, K. G.; Fenske, R. F. Inorg. Chem.

1968, 7, 1273-1284. (c) Hush, N. S.; Williams, M. I. J. Mol.

Spectrosc. 1974, 50, 349-368.

(50) Betley, T. A.; Peters, J. C. Inorg. Chem. 2003, 42, XXXXX.

5064 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

Li(TMEDA),²⁹(Ph)₂(BH₃)PCH₃,³²[Ph₂B(CH₂PPh₂)₂][Li(TMEDA)₂],⁹

[Ph₂B(CH₂PPh₂)₂][ASN],⁹[Ph₂BP₂Pt(Me)₂][ASN],⁹[Ph₂BP₂]Pt-

(Me)(CO),^9b5-azoniaspiro[4.4]nonane bromide (ASNBr),⁴⁴(COD)-

PtCl₂,⁵⁴(COD)PtMe₂,⁵⁵and [HNEt₃][BPh₄]⁵⁶were prepared by

Alkyl-substituted systems appear to be generally accessible,

at least for cases where problematic Lewis acid-base donor

adducts can be kinetically avoided in the carbanion delivery

step.

For synthetic utility, this paper has also provided protocols

for preparing lithium, thallium, and ammonium salt deriva-

tives of the bis(phosphino)borates. While detailed studies of

the reactivity of these derivatives with transition metal

precursors is reserved for future reports, we note that the

thallium and ammonium salts have proven effective to date

in our laboratories. Also, the reaction product profile can be

highly dependent on which countercation is used.

Finally, we have discussed the electron-releasing character

of these anionic phosphine ligands. While this latter issue is

not fully resolved, we can conclude that (phosphino)borates

are generally more electron-releasing than their neutral

phosphine analogues, despite the fact that the borate unit is

not delocalized by conventional resonance contributors. This

latter conclusion suggests that neutral complexes supported

by (phosphino)borate ligands will be more electron-rich than

their cationic counterparts. Whether a zwitterionic description

is most appropriate for a neutral complex supported by a

(phosphino)borate ligand obviously depends on the degree

of charge delocalization. Measuring the degree of charge

delocalization, and the electronic mechanism by which

delocalization occurs, is not reliably done through infrared

carbonyl studies. Such model studies do, however, speak to

the relatiVe electron-richness of each complex discussed

herein. At present, we suggest that a zwitterionic description

is useful if it predicts a complex’s chemical reactivity. A

diverse set of model studies have shown that neutral

complexes supported by (phosphino)borate ligands will

mediate transformations typical of their more conventional,

cationic counterparts. In this sense, our classification of these

neutral complexes as “zwitterionic” is meaningful.

i

literature methods. Pr₂PMe⁵⁷was prepared by reaction of Pr₂PCl

with MeLi and isolation of the product by distillation. Me₃P(BH₃)⁵⁸

59

was prepared by reaction of PMe₃with BH₃‚SMe₂. SPMe₃was

prepared by the addition of elemental sulfur to a toluene solution

of PMe₃and collecting the precipitate. All other chemicals were

purchased from Aldrich, Strem, Alfa Aesar, or Matrix Scientific

and used without further purification. NMR spectra were recorded

at ambient temperature on Varian Mercury 300 MHz and Inova

500 MHz and Joel 400 MHz spectrometers, unless otherwise noted.

¹H and ¹³C{¹H} NMR chemical shifts were referenced to residual

solvent as determined relative to Me₄Si (0 ppm). ³¹P{¹H} NMR,

¹¹B{¹H} NMR, and ¹⁹F{¹H} NMR chemical shifts are reported

relative to an external standard (0 ppm) of 85% H₃PO₄, neat BF₃‚

Et₂O, and neat CFCl₃, respectively. Abbreviations for reported

signal multiplicities are as follows: s, singlet; d, doublet; t, triplet;

q, quartet; m, multiplet; br, broad. IR spectra were recorded at 2

cm^-1resolution on a Bio-Rad Excalibur FTS 3000 spectrometer

controlled by Win-IR Pro software using a KBr solution cell.

Elemental analyses were performed by Desert Analytics, Tucson,

AZ. X-ray diffraction experiments were carried out by the Beck-

mann Institute Crystallographic Facility on a Bruker P4 CCD

diffractometer.

General Method A: Preparation of Me₂SnR₂. Aryl-Grignard

reagents were either purchased or generated by standard methods

using magnesium and an appropriate aryl bromide. A flask

containing the aryl Grignard reagent was cooled to -78 °C in a

dry ice/acetone bath. A 0.5 equiv amount of solid Me₂SnCl₂was

added under a counterflow of dinitrogen. (Note! Me₂SnCl₂is highly

toxic. Use appropriate precautions when handling this material.)

The reaction was stirred at -78 °C for 20 min, and then the bath

was removed and the reaction allowed to warm to rt and stir over

several hours. Volatiles were removed under reduced pressure.

Hexanes (100 mL) were added to the resulting solids, and the

suspension was filtered over Celite. Residual solids were washed

with hexanes (4 × 75 mL), and the combined organic solutions

were concentrated by rotary evaporation, providing the desired Me₂-

SnR₂as either an oil or a solid. Further purification of the product

can be achieved by crystallization or distillation under heat and

vacuum. (Note: Several of the dimethyldiaryltin complexes reported

herein have appeared previously in the literature. For those cases,

relevant citations are given. NMR data in readily available

deuterated solvents (e.g. CDCl₃, C₆D₆) are included for complete-

ness.)

Experimental Section

Unless otherwise noted, all syntheses were carried out in the

absence of water and dioxygen, using standard Schlenk and

glovebox techniques. Acetonitrile, tetrahydrofuran, diethyl ether,

dichloromethane, toluene, benzene, and petroleum ether were

deoxygenated and dried by thorough sparging with N₂gas followed

by passage through an activated alumina column. Pentane and

hexanes were deoxygenated by repeated evacuation under reduced

pressure followed by introduction of dinitrogen and were dried by

storing over 3-Å molecular sieves. p-Dioxane was dried and distilled

over sodium/benzophenone under dinitrogen at atmospheric pres-

sure. Hydrocarbon and ethereal solvents were typically tested with

a standard purple solution of sodium benzophenone ketyl in

tetrahydrofuran to confirm effective oxygen and moisture removal.

Ethanol and acetone were dried and distilled over calcium sulfate

under dinitrogen. Morpholine, TMEDA, and diethylamine were

dried and distilled from KOH under dinitrogen. Deuterated chlo-

roform, benzene, dichloromethane, THF, acetonitrile, and acetone

were purchased from Cambridge Isotope Laboratories, Inc. and were

degassed by repeated freeze-pump-thaw cycles and dried over

activated 3-Å molecular sieves prior to use. Ph₂PMe,⁵¹Ph₂PCH₂-

Li(TMEDA),^{30 t}Bu₂PCl,^{52 t}Bu₂PMe,^{53 t}Bu₂P(CH₂Li),²⁹Me₂PCH₂-

(CH₃)₂Sn(C₆H₅)₂(1).^20,21,22,23Following general method A, a

1

pale yellow oil was generated (24.3020 g, 77.6%). H NMR (300

2

MHz, CDCl₃): δ 7.54 (m), 7.36 (m), 0.53 (s, J_Sn-H) 54 Hz).

(CH₃)₂Sn(C₆H₄-p-Me)₂(2).^20,21,22,24Following general method

A, white solids were generated (12.3836 g, 96.9%). ¹H NMR (300

(52) Fild, M.; Stelzer, O.; Schmutzler, R. Inorg. Synth. 1973, 14, 4-9.

(53) Kolodiazhnyi, O. I. Synth. Meth. Organomet. Inorg. Chem. 1996, 3,

88-90.

(54) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-

428.

(55) Costa, E.; Pringle, P. G.; Ravetz, M. Inorg. Synth. 1995, 31, 284-

286.

(56) Amorose, D. M.; Lee, R. A.; Petersen, J. L. Organometallics 1991,

10, 2191-2198.

(57) Diemert, K.; Hahn, T.; Kuchen, W.; Tommes, P. Phosphorus, Sulfur,

Silicon 1993, 83, 65-76.

(58) Mente, D. C.; Mills, J. L. Inorg. Chem. 1975, 14, 1862-1865.

(59) Jones, W. D.; Selmeczy, A. D. Organometallics 1992, 11, 889-893.

(51) Seyferth, D.; Burlitch, J. M. J. Org. Chem. 1963, 28, 2463.

Inorganic Chemistry, Vol. 42, No. 17, 2003 5065

Thomas and Peters

MHz, CDCl₃): δ 7.51 (d, 4H, J_Sn-H) 45 Hz), 7.27 (d, 4H), 2.44

of volatiles under reduced pressure provided crude diarylchloro-

borane. If necessary, recrystallization from hydrocarbon solvent (e.g.

petroleum ether) at -35 °C provided pure diarylchloroborane. If

any dimethyltin dichloride was observed by ¹H NMR spectroscopy,

it was removed by vacuum sublimation.

2

(s, 6H), 0.57 (s, 6H, J_Sn-H) 55 Hz). ¹³C{¹H} NMR (75.4 MHz,

CDCl₃): δ 138.5, 137.0, 136.4 (J_Sn-C) 38 Hz), 129.3 (J_Sn-C

)

50 Hz), 21.6, -9.8 (¹J_Sn-C) 356 Hz).

(CH₃)₂Sn(C₆H₃-m,m-Me₂)₂(3). Following general method A,

1

white solids were generated (19.4541 g, 87.9%). H NMR (300

(C₆H₅)₂BCl (10).^14,15Following general method B, colorless

1

MHz, CDCl₃): δ 7.21 (s, 4H, J_Sn-H) 48 Hz), 7.05 (s, 2H), 2.38

(s, 12H), 0.55 (s, 6H, ²J_Sn-H) 55 Hz). ¹³C{¹H} NMR (75.4 MHz,

CDCl₃): δ 140.6, 137.7 (J_Sn-C) 49 Hz), 134.1 (J_Sn-C) 36 Hz),

130.5 (J_Sn-C) 11 Hz), 21.5, -9.8 (¹J_Sn-C) 360 Hz). Anal. Calcd

for C₁₈H₂₄Sn: C, 60.21; H, 6.74. Found: C, 59.95; H, 6.74.

(CH₃)₂Sn(C₆H₄-p-^tBu)₂(4).²⁵Following general method A,

crystalline solids were generated (5.403 g, 72.8%). H NMR (300

MHz, CDCl₃): δ 8.05 (d), 7.65 (t), 7.54 (t). ¹³C{¹H} NMR (75.4

MHz, CDCl₃): δ 137.2, 133.1, 128.0. ¹¹B{¹H} NMR (128.3 MHz,

CDCl₃): δ 62.8.

(p-MeC₆H₄)₂BCl (11).^15,16Following general method B, white

1

solids were generated (4.7058 g, 98.0%). H NMR (300 MHz,

1

3

white solids were generated (18.1831 g, 96.2%). H NMR (300

C₆D₆): δ 7.98 (d, 4H, J_H-H) 8.1 Hz), 7.01 (d, 4H, J_H-H) 8.1

Hz), 2.06 (s, 6H). ¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ 144.0, 138.1,

129.3, 22.0. ¹¹B{¹H} NMR (128.3 MHz, C₆D₆): δ 61.6.

MHz, C₆D₆): δ 7.51 (d, 4H), 7.32 (d, 4H), 1.24 (s, 18H), 0.45 (s,

6H, ²J_Sn-H) 54 Hz). ¹³C{¹H} NMR (125.7 MHz, CDCl₃): δ 151.6,

137.3, 136.3 (J_Sn-C) 38 Hz), 125.5 (J_Sn-C) 48 Hz), 34.8, 31.5,

-9.8 (¹J_Sn-C) 364 Hz). Anal. Calcd for C₂₂H₃₂Sn: C, 63.64; H,

7.77. Found: C, 63.53; H, 7.99.

(m,m-Me₂C₆H₃)₂BCl (12). Following general method B, white

1

solids were generated (5.3505 g, 85.6%). H NMR (300 MHz,

C₆D₆): δ 7.74 (s, 4H), 6.94 (s, 2H), 2.11 (s, 12H). ¹³C{¹H} NMR

(75.4 MHz, C₆D₆): δ 137.6, 135.5, 135.2, 21.5. ¹¹B{¹H} NMR

(128.3 MHz, C₆D₆): δ 62.6. Anal. Calcd for C₁₆H₁₈BCl: C, 74.90;

H, 7.07. Found: C, 74.59; H, 7.32.

(CH₃)₂Sn(C₆H₄-p-OMe)₂(5).^21,22,26Following general method

A, an oil which solidified upon standing was generated (13.7652

1

g, 83.3%). H NMR (300 MHz, CDCl₃): δ 7.57 (d, 4H), 7.07 (d,

2

4H), 3.94 (s, 6H), 0.61 (s, 6H, J_Sn-H) 55 Hz). ¹³C{¹H} NMR

(p-^tBuC₆H₄)₂BCl (13). Following general method B, white

crystalline solids were generated (5.2415 g, 90.6%). ¹H NMR (300

MHz, C₆D₆): δ 8.08 (d, 4H, 7.8 Hz), 7.33 (d, 4H, 7.8 Hz), 1.19 (s,

18H). ¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ 156.5, 137.7, 125.2,

35.0, 31.0. ¹¹B{¹H} NMR (128.3 MHz, C₆D₆): δ 61.8. Anal. Calcd

for C₂₀H₂₆BCl: C, 76.82; H, 8.38. Found: C, 76.00; H, 8.56.

(p-MeOC₆H₄)₂BCl (14).^15,17Following general method B, white

(75.4 MHz, CDCl₃): δ 160.3, 137.5 (J_Sn-C) 42 Hz), 131.1, 114.3

(J_Sn-C) 53 Hz), 55.1, -9.7 (¹J_Sn-C) 358 Hz).

(CH₃)₂Sn(C₆H₄-p-CF₃)₂(6).²¹Following general method A, an

orange oil was generated (14.9446 g, 94.4%). ¹H NMR (300 MHz,

C₆D₆): δ 7.40 (d, 4H), 7.19 (d, 4H, J_Sn-H) 43.8 Hz), 0.27 (s, 6H,

²J_Sn-H) 54.3 Hz). ¹⁹F NMR (282.1 MHz, C₆D₆): δ -63.5.

(CH₃)₂Sn(C₆H₄-o-OMe)₂(7).²²Following general method A,

1

solids were generated (6.2865 g, 96.5%). H NMR (300 MHz,

1

white crystalline solids were generated (16.2126 g, 98.7%). H

C₆D₆): δ 8.06 (d, 4H, J ) 8.1 Hz), 6.79 (d, 4H, J ) 8.1 Hz), 3.23

(s, 6H). ¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ 164.4, 140.2, 114.2,

55.1. ¹¹B{¹H} NMR (128.3 MHz, C₆D₆): δ 59.4. Anal. Calcd for

C₂₀H₂₆BCl: C, 64.54; H, 5.42. Found: C, 64.47; H, 5.30.

(p-CF₃C₆H₄)₂BCl (15). Following general method B, colorless

crystalline solids were generated (3.5460 g, 31.0%). ¹H NMR (300

MHz, C₆D₆): δ 7.54 (d, J_H-H) 7.5 Hz), 7.35 (d, J_H-H) 7.5 Hz).

¹⁹F NMR (282 MHz, C₆D₆): δ -63.9. ¹¹B{¹H} NMR (121.3 MHz,

C₆D₆): δ 61.5. Anal. Calcd for C₁₄H₈BClF₆: C, 49.98; H, 2.40.

Found: C, 50.37; H, 2.51.

NMR (300 MHz, C₆D₆): δ 7.52 (dd, 2H, J_Sn-H) 52.2 Hz), 7.20

(ddd, 2H), 6.94 (dt, 2H), 6.54 (br d, 2H), 3.24 (s, 6H), 0.65 (s, 6H,

²J_Sn-H) 56.1 Hz). ¹³C{¹H} NMR (75.4 MHz, CDCl₃): δ 164.0,

137.3 (J_Sn-C) 26.6 Hz), 130.2, 129.8, 121.2 (J_Sn-C) 47.4 Hz),

109.4, 55.5, -8.5 (¹J_Sn-C) 375 Hz). Anal. Calcd for C₁₆H₂₀O₂Sn:

C, 52.93; H, 5.55. Found: C, 52.20; H, 5.55.

(CH₃)₂Sn(C₆H₃-o,o-(OMe)₂)₂(8).²⁷This was prepared by the

previously reported method (deprotonation of 1,3-(dimethoxy)-

benzene followed by quenching with Me₂SnCl₂), yielding white

solids (11.3345 g, 55.8%). ¹H NMR (300 MHz, C₆D₆): δ 7.16 (t,

ⁱPr₂P(CH₂Li) (17). (Caution! This procedure eVolVes gas in a

sealed system. Use appropriate precautions, including periodic

2

4H), 6.34 (d, 4H), 3.27 (s, 6H), 0.89 (s, 6H, J_Sn-H) 58.5

t

Hz).

Venting of the Vessel to release pressure.) A solution of BuLi in

(CH₃)₂Sn(C₆H₄-o-CF₃)₂(9). Following general method A, an

amber oil was generated (19.7956 g, 90.3%). ¹H NMR (300 MHz,

C₆D₆): δ 7.48 (dd, 2H), 7.39 (br d, 4H), 6.96 (m, 4H), 0.57 (s,

6H, ²J_Sn-H) 57.0 Hz). ¹³C{¹H} NMR (75.4 MHz, CDCl₃): δ 139.6

(br), 137.9 (J_Sn-C) 26.5 Hz), 131.2 (J_Sn-C) 42.8 Hz), 129.0 (J_Sn-C

) 9.1 Hz), 126.2 (q, J_F-C) 4.5 Hz, J_Sn-C) 31.7 Hz), -6.2 (septet,

pentane (0.891 mL, 1.7M, 1.51 mmol) was placed in a 50 mL thick-

walled sealable vessel. Volatiles were removed under reduced

pressure, providing solid ^tBuLi. To the white solids was added neat

ⁱPr₂PMe (185.6 mg, 1.404 mmol). The reaction vessel was evacuated

and sealed. The reaction was heated to 60 °C for 20 h, during which

time yellow-white solids formed. The vessel was cooled to rt, and

the resulting solids were collected by filtration and washed with

petroleum ether (3 × 2 mL). The resulting white solids were dried

under reduced pressure, providing 17 (140.0 mg, 72.2%). ³¹P{¹H}

NMR (121.4 MHz, THF): δ 22.8.

1

J_F-C) 2.6 Hz, J_Sn-C) 392 Hz). ¹⁹F NMR (282.1 MHz, C₆D₆):

δ -60.4. Anal. Calcd for C₁₆H₁₄F₆Sn: C, 43.78; H, 3.21. Found:

C, 42.90; H, 3.48.

General Method B: Preparation of R₂BCl. To a thick-walled

vessel with a stir bar and sealable Teflon valve was added an

appropriate dimethyldiaryltin compound (ca. 10-15 g) and heptane

(25 mL). A 1 equiv amount of a solution of BCl₃in heptane (ca.

25 mL of a 1 M solution) was added to the vessel at rt, and the

vessel was sealed. After being stirred at rt for 30 min, the reaction

was placed in a oil bath maintained at 100 °C and was further stirred

for 24-48 h at 100 °C. The vessel was removed from the oil bath

and allowed to cool, causing dimethyltin dichloride to crystallize

from the mixture. The resulting solution was decanted from the

white crystals. (Note! Me₂SnCl₂is highly toxic. Use appropriate

precautions when handling and recoVering this material.) Removal

(p-^tBuPh)₂PCH₂Li(TMEDA) (19). A solution of n-BuLi in

hexanes (2.20 mL, 1.6 M, 3.52 mmol) was added to a stirring rt

petroleum ether solution of TMEDA (532 µL, 3.52 mmol) and (p-

^tBuPh)₂PMe (1.0990 g, 3.5176 mmol). Upon addition, the mixture

turned orange. The mixture was stirred at rt for 4 d, precipitating

a pale yellow product solid. The solids were collected by filtration

and washed with petroleum ether (2 × 2 mL). Drying the solids

under reduced pressure provided 19 as pale yellow solids (1.1358

1

g, 74.3%). H NMR (300 MHz, 10:1 C₆D₆/THF-d₈): δ 7.85 (dd,

4H), 7.22 (d, 4H), 2.20 (s, 4H), 2.05 (s, 12H), 1.22 (s, 18H), 0.06

(d, 2H). ³¹P NMR (121.4 MHz, 10:1 C₆D₆/THF-d₈): δ -1.26.

5066 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

[Ph₂B(CH₂PPh₂)₂][Et₄N] (25[TEA]). The precursor [Ph₂B(CH₂-

added to stirring 26[Li]. Immediately, a white precipitate formed.

The mixture was stirred for 15 min. The supernatant was decanted,

and the white solids were subsequently collected by filtration and

washed with Et₂O (2 × 2 mL). The solids were dried under reduced

PPh₂)₂][Li(TMEDA)] was prepared as previously described.⁹

A

solution of 25[Li] (500 mg, 0.592 mmol) in EtOH (8 mL) was

added to a stirring solution of [NEt₄][Br] (186.5 mg, 0.887 mmol)

in EtOH (4 mL) at room temperature. Within minutes, a white

precipitate formed. After 30 min, the solids were collected by

filtration. The solids were washed with EtOH (3 × 5 mL) and Et₂O

(2 × 3 mL). The solids were dried under reduced pressure providing

25[TEA] (374 mg, 91%). ¹H NMR (300 MHz, acetone-d₆): δ 7.29

(m, 4H), 7.16 (m, 8H), 6.99 (m, 12H), 6.73 (t, 4H), 6.13 (t, 2H),

3.46 (q, 8H), 1.64 (br, 4H), 1.37 (tt, 12H). ³¹P{¹H} NMR (121.4

1

pressure, providing white 26[ASN] (199.4 mg, 79.8%). H NMR

(300 MHz, acetone-d₆): δ 7.16 (m, 12H), 7.00 (m, 12H), 6.55 (d,

4H), 3.59 (m, 8H), 2.19 (m, 8H), 2.10 (s, 6H), 1.61 (br, 4H). ¹³C-

{¹H} NMR (125.7 MHz, acetone-d₆): δ 163 (q), 148.1 (d), 135.3,

133.8 (d), 130.1, 127.8, 126.9, 126.6, 63.6, 26.6 (br), 22.8, 21.4.

³¹P{¹H} NMR (121.4 MHz, acetone-d₆): δ -8.47 (q, ²J_B-P) 11.5

Hz). ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ -12.1. Anal. Calcd

for C₄₈H₅₄BNP₂: C, 80.33; H, 7.58; N, 1.95. Found: C, 78.66; H,

7.46; N, 1.81.

2

MHz, acetone-d₆): δ -8.6 (d, J_P-B) 13 Hz). ¹¹B{¹H} NMR

(128.3 MHz, acetone-d₆): δ -12.9.

[Ph₂B(CH₂PPh₂)₂][ⁿBu₄N] (25[TBA]). The precursor [Ph₂B(CH₂-

PPh₂)₂][Li(TMEDA)] was prepared as previously described.⁹Solid

25[Li] (3.51 g, 4.42 mmol) was dissolved in EtOH (20 mL). With

stirring, an EtOH solution (15 mL) of [ⁿBu₄N][Cl] (1.424 g, 4.42

mmol) was added dropwise. White solids began precipitating

immediately upon addition. After the addition was complete, the

reaction was stirred for 30 min. The white solids were collected

by filtration and washed with EtOH (30 mL) and Et₂O (50 mL).

The white solids were dried under reduced pressure, providing

25[TBA] (3.13 g, 88%). ¹H NMR (300 MHz, acetone-d₆): δ 7.29

(br, 4H), 7.17 (m, 8H), 7.00 (m, 12H), 6.73 (m, 4H), 6.61 (t, 2H),

3.42 (m, 8H), 1.81 (m, 8H), 1.65 (br, 4H), 1.41 (sextet, 8H),

[(p-^tBuPh)₂B(CH₂PPh₂)₂][Li(TMEDA)₂] (27[Li]). Solid yellow

Ph₂PCH₂Li(TMEDA) (1.9698 g, 6.1223 mmol) was suspended in

diethyl ether (100 mL) in a Schlenk flask with a stir bar and sealed

with a septum. The reaction vessel was cooled to -78 °C in a dry

ice/acetone bath. A solution of (p-^tBuPh)₂BCl (957.9 mg, 3.064

mmol) dissolved in toluene (10 mL) was introduced dropwise via

syringe to the cooled reaction flask. The reaction was stirred and

warmed gradually to rt over 4 h. Volatiles were removed under

reduced pressure providing pale yellow solids and yellow oil. The

flask was taken into the drybox, and petroleum ether (50 mL) was

added. The mixture was stirred for 10 min, and the resulting solids

were isolated on a sintered glass frit and washed with petroleum

ether (3 × 30 mL), providing pale yellow solid 27[Li] (2.2105 g,

78.9%). ¹H NMR (300 MHz, CD₃CN): δ 7.15 (m, 12H), 7.05 (m,

12H), 6.89 (d, 4H), 2.36 (s, 4H), 2.23 (s, 12H), 1.46 (br, 4H), 1.23

(s, 18H). ¹³C{¹H} NMR (125.7 MHz, CD₃CN): δ 163 (br), 147.9

(br), 144.7, 134.9, 133.7 (d), 128.3 (d),127.3, 123.2, 57.7, 46.3,

34.5, 32.1, 26.3 (br). ³¹P{¹H} NMR (121.4 MHz, CD₃CN): δ

0.97 (t, 12H). ³¹P{¹H} NMR (121.4 MHz, acetone-d₆):

δ

-8.8 (²J_P-B) 10 Hz). ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

-12.6.

{[Ph₂B(CH₂PPh₂)₂][Tl]}_n(25[Tl]). The precursor [Ph₂B(CH₂-

PPh₂)₂][Li(TMEDA)] was prepared as previously described.⁹Solid

25[Li] (284.4 mg) was dissolved in EtOH (1.5 mL). With stirring,

an EtOH solution (1.5 mL) of TlPF₆(145.3 mg, 0.416 mmol) was

added. Precipitation of off-white solids occurred as the solution

was stirred over 30 min. After 30 min, the solids were isolated by

filtration and washed with EtOH (1 mL). The solids were then

dissolved in THF (6 mL) and filtered, and from the resulting

solution, colorless 25[Tl] was crystallized by vapor diffusion of

2

-10.05 (q, J_B-P) 11.5 Hz). ¹¹B{¹H} NMR (128.3 MHz, CD₃-

CN): δ -13.3.

[(p-^tBuPh)₂B(CH₂PPh₂)₂][ASN] (27[ASN]). Solid 27[Li] (589.6

mg, 0.6451 mmol) was dissolved in ethanol (9 mL). Solid (ASN)-

Br (138.2 mg, 0.6705 mmol) was dissolved in ethanol (3 mL) and

added to stirring 27[Li]. After 5 min, a white precipitate formed.

The mixture was stirred for 30 min and allowed to settle. The

supernatant was decanted, and the white solids were subsequently

collected by filtration and washed with Et₂O (1 mL). The solids

were dried under reduced pressure, providing white 27[ASN] (357.4

mg, 68.1%). ¹H NMR (300 MHz, CD₃CN): δ 7.17 (br, 12H), 7.08

(br, 12H), 6.90 (d, 4H), 3.40 (m, 8H), 2.12 (m, 8H), 1.49 (br, 4H),

1.24 (s, 18H). ¹³C{¹H} NMR (125.7 MHz, CD₃CN): δ 162.8 (q),

148.0, 135.2, 133.9, 128.5, 127.5, 123.4, 64.0, 34.7, 32.3, 26.2 (br),

22.9. ³¹P{¹H} NMR (121.4 MHz, CD₃CN): δ -10.04. ¹¹B{¹H}

NMR (128.3 MHz, CD₃CN): δ -13.2. Anal. Calcd for C₅₄H₆₆-

BNP₂: C, 80.88; H, 8.30; N, 1.75. Found: C, 81.14; H, 8.12; N,

1.93.

1

petroleum ether (276.3 mg, 86.5%). H NMR (300 MHz, THF-

d₈): δ 7.41 (m, 8H), 7.12 (m, 16H), 6.91 (m, 6H), 2.32 (br d, 4H,

³J_Tl-H) 9.6 Hz). ³¹P{¹H} NMR (202.4 Hz, THF-d₈, 55 °C): δ

57.9. ³¹P{¹H} NMR (202.4 Hz, THF-d₈, -65 °C): δ 52.6 (br d,

¹J_Tl-P) 4166 Hz). ¹¹B{¹H} NMR (128.3 MHz, THF-d₈): δ -12.2.

Anal. Calcd for C₃₈H₃₄BP₂Tl: C, 59.44; H, 4.46. Found: C, 59.63;

H, 4.52.

[(p-MePh)₂B(CH₂PPh₂)₂][Li(TMEDA)] (26[Li]). Solid yellow

Ph₂PCH₂Li(TMEDA) (1.3999 g, 4.3510 mmol) was suspended in

diethyl ether (100 mL) in a Schlenk flask with a stir bar and sealed

with a septum. The reaction vessel was cooled to -78 °C in a dry

ice/acetone bath. A solution of (p-MePh)₂BCl (498.3 mg, 2.180

mmol) dissolved in toluene (5 mL), was introduced dropwise via

syringe to the cooled reaction flask. The reaction was stirred and

warmed gradually to rt over 14 h, providing a pale yellow

precipitate. Volatiles were removed under reduced pressure, and

the resulting solids were isolated in the drybox on a sintered glass

frit and washed with petroleum ether (3 × 30 mL), providing pale

yellow solid 26[Li] (1.1907 g, 65.7%). ¹H NMR (300 MHz,

acetone-d₆): δ 7.15 (m, 12H), 6.97 (m, 12H), 6.53 (d, 4H), 2.36

(s, 4H), 2.19 (s, 12H), 2.09 (s, 6H), 1.61 (br, 4H). ³¹P{¹H} NMR

[(p-MeOPh)₂B(CH₂PPh₂)₂][Li(TMEDA)₂] (28[Li]). Solid

yellow Ph₂PCH₂Li(TMEDA) (1.8666 g, 5.8016 mmol) was sus-

pended in diethyl ether (70 mL) in a Schlenk flask with a stir bar

and sealed with a septum. The reaction vessel was cooled to -78

°C in a dry ice/acetone bath. A solution of (p-MeOPh)₂BCl (755.9

mg, 2.902 mmol) dissolved in toluene (5 mL) was introduced

dropwise via syringe to the cooled reaction flask. The reaction was

stirred and warmed gradually to rt over 12 h. Volatiles were

removed under reduced pressure providing pale yellow solids. The

flask was taken into the drybox, and petroleum ether (20 mL) was

added. The mixture was stirred for 10 min, and the resulting solids

were isolated on a sintered glass frit and washed with diethyl ether

(2 × 10 mL), providing off-white solid 28[Li] (2.1055 g, 84.1%).

¹H NMR (300 MHz, acetone-d₆): δ 7.17 (m, 12H), 6.99 (m, 12H),

2

(121.4 MHz, acetone-d₆): δ -8.36 (q, J_B-P) 9.2 Hz). ¹¹B{¹H}

NMR (128.3 MHz, acetone-d₆): δ -12.9.

[(p-MePh)₂B(CH₂PPh₂)₂][ASN] (26[ASN]). Crude 26[Li] (289.3

mg, 0.3482 mmol) was dissolved in ethanol (4 mL). Solid (ASN)-

Br (80.4 mg, 0.390 mmol) was dissolved in ethanol (2 mL) and

Inorganic Chemistry, Vol. 42, No. 17, 2003 5067

Thomas and Peters

6.34 (d, 4H), 3.60 (s, 6H), 2.37 (s, 8H), 2.20 (s, 24H), 1.61 (br,

4H). ¹³C{¹H} NMR (125.7 MHz, acetone-d₆): δ 157 (br), 148.2

(d), 135.8, 133.7 (d), 129.3 (d), 127.8 (d), 126.5, 111.9, 58.2, 55.0,

46.2, 27 (br). ³¹P{¹H} NMR (121.4 MHz, acetone-d₆): δ -8.46

(s, 24H), 1.72 (br, 4H). ³¹P{¹H} NMR (121.4 MHz, THF): δ -9.8

(q, ²J_P-B) 9.8 Hz). ¹⁹F{¹H} NMR (282.1 MHz, THF): δ -62.3.

¹¹B{¹H} NMR (128.3 MHz, THF): δ -12.7.

[(p-CF₃Ph)₂B(CH₂PPh₂)₂][ASN] (29[ASN]). Crude 29[Li] (376.3

mg, 0.401 mmol) was dissolved in acetone along with ap-

proximately 1 equiv of (ASN)Br. The solution was stirred for 30

min, and the resulting mixture was filtered. Volatiles were removed

under reduced pressure. The solids were redissolved in a minimum

of Et₂O, and crystallization at -30 °C provided 29[ASN] (186.3

2

(q, J_B-P) 10.9 Hz). ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

-13.7.

[(p-MeOPh)₂B{CH₂P(Ph)₂(BH₃)}₂][ASN] (28‚BH₃[ASN]).

Colorless oil MePPh₂(BH₃) (0.9615 g, 4.492 mmol) was dissolved

in Et₂O (100 mL) in a Schlenk flask with a stir bar and sealed with

a septum. The flask was cooled to -78 °C in a dry ice/acetone

bath. To the stirring reaction was added a solution of s-BuLi in

cyclohexane (3.5 mL, 1.3M, 4.6 mmol). The reaction was stirred

and maintained at -78 °C for 3 h. After 3 h, a toluene solution (5

mL) of (p-MeOPh)₂BCl (585.9 mg, 2.249 mmol) was added by

syringe, causing the rapid formation of white solids. The reaction

was stirred and allowed to gradually warm to rt over 14 h. Volatiles

were removed under reduced pressure, providing white solids. (³¹P-

{¹H} NMR analysis of a portion of the crude reaction in THF

showed the formation of a single product.) The white solids were

dissolved in EtOH (10 mL). With stirring, an EtOH solution (4

mL) of (ASN)Br (469.3 mg, 2.277 mmol) was added slowly, and

white precipitate formed immediately. The mixture was stirred for

20 min. The solids were collected by filtration and washed with

EtOH (2 mL). The solids were dried under reduced pressure,

1

mg, 56.3%). H NMR (300 MHz, acetone-d₆): δ 7.30 (br, 4H),

7.17 (br, 8H), 7.01 (m, 12H), 6.96 (m, 4H), 3.73 (m, 8H), 2.27 (m,

8H), 1.72 (br, 4H). ¹³C{¹H} NMR (75.4 MHz, acetone-d₆): δ 146.9,

135.1, 133.7 (d), 128.1, 127.0, 124.0 (q), 122.4, 63.7, 25 (br), 22.8.

³¹P{¹H} NMR (121.4 MHz, acetone-d₆): δ -10.04. ¹⁹F{¹H} NMR

(282.1 MHz, acetone-d₆): δ -61.5. ¹¹B{¹H} NMR (128.3 MHz,

acetone-d₆): δ -11.3. Anal. Calcd for C₄₈H₄₈BF₆NP₂: C, 69.83;

H, 5.86; N, 1.70. Found: C, 68.28; H, 5.85; N, 1.84.

[Cy₂B(CH₂PPh₂)₂][Li(TMEDA)₂] (30[Li]). Solid yellow Ph₂-

PCH₂Li(TMEDA) (1.4744 g, 4.5739 mmol) was suspended in

diethyl ether (100 mL) in a Schlenk flask with a stir bar and sealed

with a septum. The reaction vessel was cooled to -78 °C in a dry

ice/acetone bath. A solution of Cy₂BCl (491.6 mg, 2.312 mmol)

dissolved in toluene (5 mL), was introduced dropwise via syringe

to the cooled reaction flask. The reaction was stirred and warmed

gradually to rt over 14 h, providing a pale yellow precipitate.

Volatiles were removed under reduced pressure, and the resulting

solids were isolated by filtration and washed with petroleum ether

(3 × 30 mL), providing pale yellow solid 30[Li] (1.2134 g, 64.4%).

Crystallization from toluene at -30 °C provided analytically pure

1

providing analytically pure 28‚BH₃[ASN] (1.6137 g, 92.3%). H

NMR (300 MHz, acetone-d₆): δ 7.45 (m, 8H), 7.12 (m, 12H), 6.88

(br d, 4H), 6.10 (d, 4H), 3.69 (m, 8H), 3.57 (s, 6H), 2.24 (m, 8H),

2.2 (br d, 4H), 0.5-1.6 (br, 6H). ¹³C{¹H} NMR (125.7 MHz,

acetone-d₆): δ 155.7, 153 (br), 137.9 (d), 135.2, 132.4 (d), 128.4,

127.3 (d), 110.8, 69.3, 63.7, 22.8, 20.5 (br). ³¹P{¹H} NMR (121.4

MHz, acetone-d₆): δ 21.3. ¹¹B{¹H} NMR (128.3 MHz, acetone-

d₆): δ -13.2, -36.0. Anal. Calcd for C₄₈H₆₀B₃NO₂P₂: C, 74.16;

H, 7.78; N, 1.80. Found: C, 74.36; H, 7.89; N, 1.90.

1

30[Li]. H NMR (300 MHz, acetone-d₆): δ 7.39 (m, 8H), 7.09

(m, 12H), 2.34 (s, 8H), 2.17 (s, 24H), 1.63 (br d, 4H), 1.47 (br d,

4H), 0.8-1.2 (m, 16H), 0.31 (m, 2H). ¹³C{¹H} NMR (125.7 MHz,

acetone-d₆): δ 149.3 (d), 133.9 (d), 217.8 (d), 126.6, 69.3, 58.3,

46.1, 37 (br), 32.6, 31.0, 22 (br). ³¹P{¹H} NMR (121.4 MHz,

acetone-d₆): δ -6.18. ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

-13.1. Anal. Calcd for C₅₀H₇₈BLiN₄P₂: C, 73.70; H, 9.10; N, 6.50.

Found: C, 74.10; H, 9.65; N, 6.88.

[Ph₂B(CH₂P{p-^tBuPh}₂)₂][Li(TMEDA)_x] (31[Li]). The same

method as for 26[Li] yielded pale yellow solids, 0.9618 g, 75.8%.

¹H NMR (300 MHz, acetone-d₆): δ 7.25 (br, 4H), 7.15 (m, 8H),

7.05 (m, 8H), 6.67 (t, 4H), 6.57 (t, 2H), 2.36 (s, 4H), 2.20 (s, 12H),

1.66 (br, 4H), 1.23 (s, 36H). ¹³C{¹H} NMR (125.7 MHz, acetone-

d₆): δ 166.3 (br), 148.8, 144.5, 135.2, 133.4, 125.7, 124.5, 121.9,

58.2, 46.1, 34.8, 31.7, 26.0 (br). ³¹P{¹H} NMR (121.4 MHz,

acetone-d₆): δ -12.40. ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆):

δ -12.2.

[Ph₂B(CH₂P{p-^tBuPh}₂)₂][ASN] (31[ASN]). The same method

as for 26[Li] yielded white solids, 0.6900 g, 80.0%. ¹H NMR (300

MHz, acetone-d₆): δ 7.25 (br, 4H), 7.15 (dd, 8H), 7.05 (d, 8H),

6.67 (t, 4H), 6.56 (t, 2H), 3.77 (m, 8H), 2.30 (br, 4H), 2.05 (m,

8H), 1.24 (s, 36H). ³¹P{¹H} NMR (121.4 MHz, acetone-d₆): δ

-12.36. Anal. Calcd for C₆₂H₈₂BNP₂: C, 81.47; H, 9.04; N, 1.53.

Found: C, 81.07; H, 9.36; N, 1.50.

[(p-MeOPh)₂B(CH₂P{p-^tBuPh}₂)₂][Li(TMEDA)_x] (32[Li]). Solid

19 (509.3 mg, 1.172 mmol) was suspended in Et₂O (20 mL) in a

Schlenk flask with a stir bar and septum. The reaction vessel was

cooled to -78 °C under dinitrogen using a dry ice/acetone bath. A

toluene solution (3 mL) of (p-MeOPh)₂BCl (153.0 mg, 0.5873

mmol) was added to the stirring cold reaction by syringe. The

reaction was stirred and gradually warmed over 12 h. Volatiles were

removed under reduced pressure, providing a tan oil. The products

were dissolved in toluene (30 mL) and filtered. The solution was

concentrated, and addition of petroleum ether caused white solid

[(p-MeOPh)₂B(CH₂PPh₂)₂][ASN] (28[ASN]). Solid 28‚BH₃-

[ASN] (393.8 mg, 0.5066 mmol) was suspended in morpholine (10

mL). The reaction was stirred and heated to 60 °C for 72 h. ³¹P-

{¹H} NMR analysis of the reaction showed the formation of

predominantly one major product and several (ca. 5) minor side

products. Volatiles were removed under reduced pressure. The

resulting solids were washed with toluene (2 × 1 mL) and Et₂O (2

× 1 mL). Drying under reduced pressure provided a white foam

1

(215.7 mg, 56.8%). H NMR (300 MHz, acetone-d₆): δ 7.17 (m,

12H), 7.00 (m, 12H), 6.35 (d, 4H), 3.66 (m, 8H), 3.61 (s, 6H),

2.22 (m, 8H), 1.60 (br, 4H). ¹³C{¹H} NMR (125.7 MHz, acetone-

d₆): δ 157.5 (br q), 148.2 (d), 135.9, 133.9, 133.8, 127.8, 126.6,

111.9, 63.7, 55.0, 27 (br), 22.8. ³¹P{¹H} NMR (121.4 MHz, acetone-

d₆): δ -8.4. ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ -12.4.

[(p-CF₃Ph)₂B(CH₂PPh₂)₂][Li(TMEDA)₂] (29[Li]). Solid pale

yellow Ph₂PCH₂Li(TMEDA) (2.0950 g, 6.5115 mmol) was sus-

pended in diethyl ether (70 mL) in a Schlenk flask equipped with

a stir bar and sealed with a septum. The flask was cooled to -78

°C in a dry ice/acetone bath under a positive pressure of dinitrogen.

Solid 15 (1.1011 g, 3.2725 mmol) was dissolved in toluene (8 mL),

and the solution was added dropwise by syringe over 5 min to the

cooled flask. The reaction became brown as it was stirred at -78

°C for 2 h. The flask was allowed to warm gradually and stir for

an additional 3 h. Volatiles were removed under reduced pressure,

providing brown solids. Toluene (8 mL) was added to the solids,

providing a heterogeneous mixture. The supernatant was decanted,

and the resulting solids were washed with petroleum ether (3 × 5

mL) and dried under reduced pressure, providing crude 29[Li]

1

(2.3626 g, 77.3%). H NMR (300 MHz, acetone-d₆): δ 7.28 (br,

4H), 7.17 (br, 8H), 7.00 (m, 12H), 6.94 (d, 4H), 2.36 (s, 8H), 2.19

5068 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

1

32[Li] to precipitate upon standing (272.6 mg, 47.8%). H NMR

(300 MHz, C₆D₆): δ 7.54 (br d, 4H), 7.46 (m, 8H), 7.16 (d, 8H),

6.72 (d, 4H), 3.47 (6H), 2.22 (br, 4H), 1.68 (br, 12H), 1.4 (br, 4H),

1.25 (36H). ¹³C{¹H} NMR (125.7 MHz, C₆D₆): δ 157 (br), 156.6,

150.5, 139.7, 134.9, 133.7 (m), 125.3, 112.8, 57.0, 55.0, 46.5, 34.9,

31.8, 24 (br d). ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ -13.4. ¹¹B-

{¹H} NMR (128.3 MHz, C₆D₆): δ -13.4.

again to -78 °C. A toluene solution (8 mL) of Ph₂BCl (1.1950 g,

5.9607 mmol) was added dropwise via syringe to the cooled

reaction, and the mixture was allowed to stir and warm gradually

over 4 h. Volatiles were removed under reduced pressure, providing

white solids. The solids were collected on a frit and washed with

diethyl ether (3 × 10 mL), providing 34 (3.3948 g, 97.8%). The

material can be crystallized from pentane vapor diffusion into a

benzene solution, providing analytically pure [Ph₂B(CH₂P(CH₃)₂-

(BH₃))₂][Li(TMEDA)]. ¹H NMR (300 MHz, C₆D₆): δ 7.69 (d, 4H),

7.36 (tt, 4H), 7.20 (tt, 2H), 2.04 (s, 12H), 1.93 (s, 4H), 1.60 (d,

4H), 0.80 (d, 12H). ¹³C{¹H} NMR (125.7 MHz, C₆D₆): δ 164 (q,

ipso B(C₆H₅)₂), 134.7, 127.2, 124.0, 57.4, 46.7, 22.7 (m), 15.0 (d).

³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 1.23 (m). ¹¹B{¹H} NMR

(128.3 MHz, C₆D₆): δ -13.3 (s, Ph₂BP₂), -34.2 (d, Ph₂B(P(BH₃))₂,

¹J_P-B) 71 Hz). ES MS (CH₃CN) (m/z): calcd for C₁₈H₃₂B₃P₂,

343.2; found, 343.2. Anal. Calcd for C₂₄H₄₈B₃LiN₂P₂: C, 61.86;

H, 10.38; N, 6.01. Found: C, 61.84; H, 10.47; N, 5.54.

[Ph₂B{CH₂P(p-CF₃Ph)₂(BH₃)}₂][Li(THF)_x] (33‚BH₃[Li]). A

diethyl ether solution (100 mL) of MeP(p-CF₃Ph)₂(BH₃) (1.3411

g, 3.8312 mmol) was placed in a Schlenk flask with a stir bar and

a septum and cooled to -78 °C in a dry ice/acetone bath. A solution

of sec-butyllithium in cyclohexane (3.0 mL, 1.3 M, 3.9 mmol) was

added by syringe, and the reaction was stirred and maintained at

-78 °C. After 3 h, a toluene solution (6 mL) of Ph₂BCl was added

by syringe to the reaction. The resulting mixture was stirred and

allowed to gradually warm over 12 h. Volatiles were removed under

reduced pressure, providing a pale yellow foam. The foam was

dissolved in THF (10 mL) and transferred into a 20 mL scintillation

vial. Volatiles were removed under reduced pressure, and the

resulting foam was washed with petroleum ether (2 × 5 mL). The

solids were dissolved in diethyl ether (12 mL) and filtered over

Celite. Removal of volatiles under reduced pressure provided crude

[Ph₂B(CH₂P(CH₃)₂(S))₂][Li(TMEDA)] (35). Solid SPMe₃(494.4

mg, 4.571 mmol) and liquid TMEDA (542.9 mg, 4.672 mmol) were

dissolved in diethyl ether (100 mL) in a Schlenk flask equipped

with a stir bar and septum. The flask was cooled to -78 °C in a

dry ice/acetone bath. A solution of n-butyllithium (2.86 mL, 1.6M,

4.58 mmol) was added dropwise via syringe to the reaction. The

reaction was stirred at -78 °C for 3 h. A toluene solution (5 mL)

of Ph₂BCl (464.3 mg, 2.316 mmol) was added dropwise via syringe

to the cooled reaction, and the mixture was allowed to stir and

warm gradually over 12 h. Volatiles were removed under reduced

pressure, providing white solids. The solids were collected by

filtration and washed with petroleum ether (3 × 10 mL), providing

white solids. Crystallization from Et₂O at -30 °C provided

analytically pure 35 (1.3138 g, 91.7%). ¹H NMR (300 MHz,

acetone-d₆): δ 7.34 (br, 4H), 7.02 (tt, 4H), 6.88 (tt, 2H), 2.35 (s,

4H), 2.17 (s, 12H), 1.74 (br d, 4H), 1.04 (d, 12H, J_P-H) 12.9

Hz). ¹³C{¹H} NMR (125.7 MHz, acetone-d₆): δ 163 (br), 134.8,

126.9, 123.7, 58.3, 46.1, 35 (br), 24.0 (d, ¹J_P-C) 51 Hz). ³¹P{¹H}

NMR (121.4 MHz, acetone-d₆): δ 43.4. ¹¹B{¹H} NMR (128.3

MHz, acetone-d₆): δ -12.5. Anal. Calcd for C₃₀H₅₈BN₄P₂S₂: C,

57.37; H, 8.43; N, 5.58. Found: C, 57.20; H, 8.34; N, 5.76.

[Ph₂B(CH₂PⁱPr₂)₂][Li(THF)₂] (36[Li]). Solid white ⁱPr₂P(CH₂-

Li) (474.2 mg, 3.433 mmol) was dissolved in THF (3 mL), creating

a yellow solution. Separately, Ph₂BCl was dissolved in Et₂O (7

mL) and added slowly to the stirring reaction. The resulting cloudy

yellow mixture was stirred for 30 min. The reaction was allowed

to settle, and the solution was decanted. Removal of the volatiles

under reduced pressure provided a yellow oil. The oil was washed

with petroleum ether (2 × 2 mL) and redissolved in Et₂O (6 mL).

Repeated crystallization and concentration of the Et₂O solution at

-30 °C provided several crops of colorless crystals of 36[Li] (387.2

mg, 39.1%). ¹H NMR (300 MHz, C₆D₆): δ 7.87 (br, 4H), 7.35 (t,

4H), 7.14 (m, 2H), 3.33 (m, 8H), 1.72 (d of septet, 4H), 1.40 (br,

4H), 1.23 (m, 8H), 1.08 (m, 12H), 0.97 (m, 12H). ¹³C{¹H} NMR

(75.4 MHz, C₆D₆): δ 167 (br), 134.2, 127.4, 123.6, 69.0, 25.7,

24.4, 22.1 (d), 22.0 (d), 20.0 (d), 19.9 (d), 18 (br). ³¹P{¹H} NMR

1

33‚BH₃[Li] (1.3756 g). H NMR (300 MHz, acetone-d₆): δ 7.64

(t, 8H), 7.50 (d, 8H), 6.90 (br, 4H), 6.46 (m, 6H), 3.62 (m, THF),

2.39 (br d, 4H), 1.79 (m, THF), 0.7-1.7 (br, 6H). ¹³C{¹H} NMR

(125.7 MHz, acetone-d₆): δ 142.6 (d), 135.1, 133.6 (d), 130.8 (q),

125.8, 125.0 (m), 123.0, 68.1 (THF), 26.2 (THF), 19 (br). ³¹P{¹H}

NMR (121.4 MHz, acetone-d₆): δ 24.0. ¹⁹F{¹H} NMR (282.1 MHz,

acetone-d₆): δ -63.2. ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

-13.0, -35.6 (br).

[Ph₂B(CH₂P{p-CF₃Ph}₂)₂][ASN] (33[ASN]). Crude 33‚BH₃[Li]

(485.6 mg, 0.514 mmol) was dissolved in CH₂Cl₂(2 mL). With

stirring, a CH₂Cl₂solution (2 mL) of (ASN)Br (106.2 mg, 0.515

mmol) was added. After 20 min, the hazy solution was filtered

over Celite, washing with CH₂Cl₂(1 mL). The combined organic

layers were dried under reduced pressure, providing a pale yellow

foam. The foam was redissolved in CH₂Cl₂(2 mL) and filtered

over Celite, washing with CH₂Cl₂(1 mL). The combined organic

layers were dried under reduced pressure, providing a pale yellow

foam, which was subjected to the filtration procedure one additional

time. The resultant foam was dissolved in neat morpholine (2 mL)

and heated to 60 °C for 12 h. Examination of an aliquot by ³¹P

NMR spectroscopy showed the formation of one dominant product.

Volatiles were removed under reduced pressure, and the yellow

oil was washed with diethyl ether (3 × 2 mL), providing white

solids. Crystallization of the white solids from THF/petroleum ether

provided analytically pure 33[ASN] (210.6 mg, 42.6%). ¹H NMR

(300 MHz, acetone-d₆): δ 7.32 (m 16H), 7.15 (br d, 4H), 6.69 (t,

4H), 6.61 (m, 2H), 3.75 (m, 8H), 2.28 (m, 8H), 1.75 (br s, 4H).

¹³C{¹H} NMR (125.7 MHz, acetone-d₆): δ 152.4 (d), 134.9, 134.1

(m), 128.7 (q), 126.2, 124.7 (d), 122.7, 63.6, 24.9 (br), 22.8. ³¹P-

{¹H} NMR (121.4 MHz, acetone-d₆): δ -6.74. ¹⁹F{¹H} NMR (282

MHz, acetone-d₆): δ -62.7. ¹¹B{¹H} NMR (128.3 MHz, acetone-

d₆): δ -12.2. Anal. Calcd for C₅₀H₄₆BF₁₂NP₂: C, 62.45; H, 4.82;

N, 1.46. Found: C, 62.40; H, 4.94; N, 1.69.

2

(121.4 MHz, C₆D₆): δ 4.94 (q, J_P-B) 63 Hz). ¹¹B{¹H} NMR

(128.3 MHz, C₆D₆): δ -13.3. Anal. Calcd for C₃₀H₅₀BLiOP₂: C,

71.15; H, 9.95. Found: C, 70.18; H, 9.65.

[Ph₂B(CH₂P(CH₃)₂(BH₃))₂][Li(TMEDA)] (34). Solid PMe₃‚

BH₃(1.0713 g, 11.915 mmol) and TMEDA (1.3893 g, 11.955

mmol) were dissolved in diethyl ether (100 mL) in a 250 mL

Schlenk flask equipped with a stir bar and septum under dinitrogen.

The flask was cooled to -78 °C in a dry ice/acetone bath. A 1.6

M solution of n-butyllithium (7.6 mL, 12 mmol) was added

dropwise via syringe to the reaction. The reaction stirred and

warmed gradually to ambient temperature over 12 h and was cooled

[Ph₂B(CH₂P^tBu₂)₂][Li(OEt₂)] (37[Li]). An Et₂O suspension

(200 mL) of ^tBu₂PCH₂Li (16) (7.3328 g, 44.14 mmol) was cooled

in a Schlenk flask with a stir bar and a septum to -78 °C in a dry

ice/acetone bath. An Et₂O solution (50 mL) of Ph₂BCl (4.4240 g,

22.07 mmol) was added to the stirring reaction. The bath was

removed, and the reaction was allowed to warm and stir for 12 h.

Volatiles were removed under reduced pressure. The mixture was

Inorganic Chemistry, Vol. 42, No. 17, 2003 5069

Thomas and Peters

dissolved in a minimum of Et₂O, removing LiCl solids by filtration.

Crystallization of the Et₂O solution at -30 °C provided 37[Li] (4.28

g, 39.6%). ¹H NMR (300 MHz, C₆D₆): δ 8.07 (br d, 4H), 7.23 (t,

4H), 7.00 (t, 2H), 2.79 (q, 4H), 1.51 (br, 4H), 1.15 (d, 36H, ³J_P-H

) 10.5 Hz), 0.66 (t, 6H). ¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ

167 (br), 135.6, 127.0, 123.3, 65.8, 32.3 (m), 31.2 (m), 18 (br),

-13.6. Anal. Calcd for C₅₀H₆₀BNP₂Pt: C, 63.69; H, 6.41; N, 1.49.

Found: C, 63.43; H, 6.74; N, 1.76.

[[(p-^tBuPh)₂B(CH₂PPh₂)₂]Pt(Me)₂][ASN] (41). Following gen-

eral method C, white solids were generated (172.3 mg, 94.4%). ¹H

NMR (300 MHz, acetone-d₆): δ 7.40 (tt, 8H), 7.06 (m, 12H), 6.83

(br d, 4H), 6.70 (d, 4H), 3.69 (m, 8H), 2.25 (m, 8H), 2.00 (br, 4H),

1.22 (s, 18H), 0.07 (“t”, 6H, Pt(CH₃)₂, J_Pt-H) 67 Hz). ¹³C{¹H}

2

14.9. ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 32.11 (q, J_B-P) 55

Hz). ¹¹B{¹H} NMR (128.3 MHz, C₆D₆): δ -12.3. Anal. Calcd

for C₃₄H₆₀BLiOP₂: C, 72.34; H, 10.71. Found: C, 72.10; H, 10.45.

NMR (125.7 MHz, acetone-d₆): δ 163 (br q), 144.3, 141.0, 135.2,

133.9, 129.0, 128.1, 123.9, 64.6, 35.2, 33.1, 23.8 (br), 23.7, 6.2

(dd, Pt(CH₃)₂, ¹J_Pt-C) 600 Hz, ²J_P-C) 9, 100 Hz). ³¹P{¹H} NMR

(121.4 MHz, acetone-d₆): δ 20.74. ¹¹B{¹H} NMR (128.3 MHz,

acetone-d₆): δ -14.2. Anal. Calcd for C₅₆H₇₂BNP₂Pt: C, 65.49;

H, 7.07; N, 1.36. Found: C, 65.68; H, 6.94; N, 1.30.

[[(p-MeOPh)₂B(CH₂PPh₂)₂]Pt(Me)₂][ASN] (42). Following

general method C, 42 was generated. ¹H NMR (300 MHz, acetone-

d₆): δ 7.40 (m, 8H), 7.09 (m, 12H), 6.78 (br d, 4H), 6.28 (m, 4H),

3.63 (m, 8H), 3.62 (s, 6H), 2.21 (m, 8H), 1.90 (br d, 4H), 0.09 (dd,

t

[(m,m-Me₂Ph)₂B(CH₂P^tBu₂)₂][Li(OEt₂)] (38[Li]). Solid Bu₂-

PCH₂Li (16) (562.6 mg, 3.385 mmol) was dissolved in a mixture

of THF and diethyl ether (3 mL/7 mL). With stirring, a diethyl

ether solution (5 mL) of (m,m-Me₂Ph)₂BCl (436.5 mg, 1.701 mmol)

was added dropwise. The resulting mixture was stirred for 14 h.

Volatiles were removed under reduced pressure. The resulting solids

were dissolved in minimal diethyl ether, and the cloudy solution

was filtered. Crystallization at -30 °C provided colorless crystalline

2

3

1

6H, Pt-CH₃, J_Pt-H) 68 Hz, J_P-H) 6, 6 Hz). ¹³C{¹H} NMR

(125.7 MHz, acetone-d₆): δ 159 (br), 140.8, 134.9, 134.7, 129.8,

128.7, 127.9, 112.9, 64.4, 55.7, 24 (br), 23.4, 6.1 (dd, Pt-CH₃, ¹J_Pt-C

38[Li] (434.6 mg, 41.4%). H NMR (500 MHz, THF-d₈): δ 7.18

(s, 4H), 6.24 (s, 2H), 3.34 (q, 6H), 2.07 (s, 12H), 1.08 (t, 4H), 0.83

(d, 36H), 0.73 (br, 4H). ¹³C{¹H} NMR (125.7 MHz, THF-d₈): δ

167.3 (q, ¹J_B-C) 51 Hz), 135.5, 132.4, 123.3, 68.4, 32.1 (d), 31.7

(d), 26.5, 22.4, 21 (br). ³¹P{¹H} NMR (121.4 MHz, THF-d₈): δ

32.67. ¹¹B{¹H} NMR (128.3 MHz, THF-d₈): δ -12.3. Anal. Calcd

for C₃₈H₆₈BLiOP₂: C, 73.54; H, 11.04. Found: C, 73.16; H, 11.26.

) 605 Hz, J_P-C) 10, 100 Hz). ³¹P{¹H} NMR (121.4 MHz,

2

acetone-d₆): δ 20.49 (¹J_Pt-P) 1893 Hz). ¹¹B{¹H} NMR (128.3

MHz, acetone-d₆): δ -13.7.

[[(p-CF₃Ph)₂B(CH₂PPh₂)₂]Pt(Me)₂][ASN] (43). Following gen-

1

eral method C, 43 was generated. H NMR (300 MHz, acetone-

[(m,m-Me₂Ph)₂B(CH₂P^tBu₂)₂][Tl] (38[Tl]). Solid 38[Li]

(104.3 mg, 0.1683 mmol) was dissolved in toluene (4 mL), forming

a colorless solution. Thallium nitrate (49.0 mg, 0.184 mmol) was

added to the reaction, and the mixture was stirred for 14 h. The

reaction was filtered, and volatiles were removed from the resulting

yellow solution under reduced pressure, providing yellow solids.

The solids were washed with petroleum ether (2 × 2 mL) and dried

d₆): δ 7.40 (m, 8H), 7.10 (m, 12H), 6.95 (m, 8H), 3.74 (m, 8H),

2

2.27 (m, 8H), 2.01 (br, 4H), 0.07 (“t”, 6H, Pt(CH₃)₂, J_Pt-H) 68

3

Hz, J_P-H) 6.3 Hz). ¹³C{¹H} NMR (75.4 MHz, acetone-d₆): δ

172 (br q), 139.4 (m), 134.2 (m), 133.3, 128.5, 127.4 (m), 124.0

1

(q), 122.7, 63.7, 22.8, 22.7 (br), 5.5 (dd, Pt(CH₃)₂, J_Pt-C) 600

2

Hz, J_P-C) 9.7, 103 Hz). ³¹P{¹H} NMR (121.4 MHz, acetone-

d₆): δ 19.33 (J_Pt-P) 1880 Hz). ¹⁹F{¹H} NMR (282.1 MHz,

acetone-d₆): δ -61.6. ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

-13.5.

1

under reduced pressure, providing 38[Tl] (109.2 mg, 87.2%). H

NMR (300 MHz, C₆D₆): δ 7.55 (s, 4H), 6.75 (s, 2H), 2.64 (br d,

3

4H), 2.35 (s, 12H), 1.05 (d, 36H, J_P-H) 12 Hz). ¹³C{¹H} NMR

[[Cy₂B(CH₂PPh₂)₂]Pt(Me)₂][Li(TMEDA)₂] (44). Following

general method C, 44 was generated. ¹H NMR (300 MHz, C₆D₆):

δ 7.92 (m, 8H), 7.14 (m, 12H), 2.21 (s, 8H), 1.88 (m, 32H), 1.3-

(125.7 MHz, C₆D₆): δ 165 (br), 135.2, 131.9, 125.4, 36.0, 30.9,

22.6, 13.0 (br). ³¹P{¹H} NMR (121.4 MHz, C₆D₆): δ 132.3 (d,

¹J_Tl-P) 6334 Hz). ¹¹B{¹H} NMR (128.3 MHz, C₆D₆): δ -12.5.

Anal. Calcd for C₃₄H₅₈BP₂Tl: C, 54.89; H, 7.86. Found: C, 55.25;

H, 8.10.

2

1.6 (m, 24H), 1.09 (m, 2H), 0.21 (br s, 6H, Pt-CH₃, J_Pt-H) 54

Hz). ¹³C{¹H} NMR (75.4 MHz, C₆D₆): δ 141 (m), 135.0 (m),

128.9, 127.9 (m), 68.2, 56.3, 45.3, 39.8 (br), 33.5, 31.4, 19.7 (br),

General Method C: Preparation of Bis(phosphino)borate-

Platinum Dimethyl Complexes [[R₂B(CH₂PR′₂)₂]PtMe₂][X]]

(40-48). A solution of CODPtMe₂in THF was added to a stirring

solution or suspension of 1 equiv of the bis(phosphino)borate in

THF. After 1 h, the reaction had gone to completion, as evinced

by a ³¹P NMR spectrum of a homogeneous reaction aliquot. The

resulting solution was concentrated to dryness under reduced

pressure. The resulting white or off-white solids were typically

washed repeatedly with Et₂O or petroleum ether to remove residual

cyclooctadiene and then were dried under reduced pressure. Purity

was assessed by examination of the NMR spectra (¹H, ¹³C, ³¹P,

¹¹B). Yields are reported for compounds where greater than 100

mg was isolated.

1

2

2.2 (dd, Pt(CH₃)₂, J_Pt-C) 530 Hz, J_P-C) 8.9, 96 Hz). ³¹P{¹H}

NMR (121.4 MHz, C₆D₆): δ 17.39 (¹J_Pt-P) 2037 Hz). ¹¹B{¹H}

NMR (128.3 MHz, C₆D₆): δ -13.2.

[[Ph₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)₂][ASN] (45). Following gen-

eral method C, white solids were generated (108.5 mg, 98.6%). ¹H

NMR (300 MHz, C₆D₆): δ 7.86 (t, 8H, J ) 8.4 Hz), 7.24 (br d,

4H, J ) 7.2 Hz), 7.17 (d, 8H, J ) 7.8 Hz), 6.76 (m, 4H), 6.70 (m,

2H), 2.53 (br d, 4H), 1.65 (m, 8H), 1.29 (s, 36H), 0.85 (m, 8H),

0.65 (s, 6H, Pt(CH₃)₂, ²J_Pt-H) 67 Hz). ¹³C{¹H} NMR (125.7 MHz,

C₆D₆): δ 166.9 (q, J_B-C) 54 Hz), 150.6, 137.0 (m), 134.6 (m),

133.2, 126.4, 124.3, 121.8, 62.3, 34.9, 32.0, 23.4 (br), 21.8, 6.6

1

2

(dd, Pt(CH₃)₂, J_Pt-C) 595 Hz, J_P-C) 9.7, 103 Hz). ³¹P{¹H}

NMR (121.4 MHz, C₆D₆): δ 16.22 (¹J_Pt-P) 1890 Hz). ¹¹B{¹H}

NMR (128.3 MHz, C₆D₆): δ -14.6. Anal. Calcd for C₆₄H₈₈BNP₂-

Pt: C, 67.47; H, 7.79; N, 1.23. Found: C, 67.47; H, 7.55; N, 1.07.

[[(p-MeOPh)₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)₂][Li(TMEDA)] (46).

[[(p-MePh)₂B(CH₂PPh₂)₂]Pt(Me)₂][ASN] (40). Following gen-

eral method C, off-white solids were generated (209.7 mg, 96.7%).

¹H NMR (300 MHz, acetone-d₆): δ 7.38 (m, 8H), 7.11 (m, 4H),

7.05 (m, 8H), 6.79 (d, 4H), 6.47 (d, 4H), 3.67 (m, 8H), 2.24 (m,

8H), 2.09 (s, 6H), 1.91 (br, 4H), 0.08 (t, 6H, Pt(CH₃)₂, ³J_P-H) 6.0

1

Following general method C, 46 was generated. H NMR (300

MHz, acetone-d₆): δ 7.35 (8H, m), 7.10 (8H, d), 6.75 (4H, d),

6.25 (4H, d), 3.61 (6H, s), 2.36 (4H, s), 2.18 (12H, s), 1.88 (4H,

2

Hz, J_Pt-H) 67 Hz). ¹³C{¹H} NMR (125.7 MHz, acetone-d₆): δ

bd), 1.29 (36H, s), 0.10 (t, 6H, Pt(CH₃)₂, ²J_Pt-H) 67 Hz, ³J_P-H

)

163 (q), 140.8 (d), 134.7, 134.1, 130.5, 128.5, 127.9, 127.6, 64.2,

1

2

5 Hz). ¹³C{¹H} NMR (125.7 MHz, acetone-d₆): δ 158 (br), 156.1,

150.4, 134.3 (m), 134.1, 124.1 (m), 112.1, 59.7, 46.2, 35.0, 31.9,

24 (br), 5.2 (dd, Pt(CH₃)₂). ³¹P{¹H} NMR (121.4 MHz, acetone-

23.4 (br), 23.3, 21.7, 5.9 (dd, Pt(CH₃)₂, J_Pt-C) 600 Hz, J_P-C

)

9.2, 103 Hz). ³¹P{¹H} NMR (121.4 MHz, acetone-d₆): δ 20.70

(¹J_Pt-P) 1895 Hz). ¹¹B{¹H} NMR (128.3 MHz, acetone-d₆): δ

5070 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

2

d₆): δ 15.95 (¹J_Pt-P) 2033 Hz). ¹¹B{¹H} NMR (128.3 MHz,

acetone-d₆): δ -14.2.

15.94 (¹J_Pt-P) 1645 Hz, J_P-P) 32 Hz). ¹¹B{¹H} NMR (128.3

MHz, CD₂Cl₂): δ -15.1. IR (CH₂Cl₂): ν_CO) 2094 cm^-1

.

[[Ph₂B(CH₂P{p-CF₃Ph}₂)₂]Pt(Me)₂][ASN] (47). Following gen-

eral method C, 47 was generated. H NMR (300 MHz, CD₃CN):

[(p-MeOPh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (52). Following general

method D, 52 was generated. H NMR (300 MHz, CD₂Cl₂): δ

1

δ 7.50 (m, 8H), 7.40 (m, 8H), 6.75 (br, 4H), 6.65 (m, 6H), 3.38

7.2-7.4 (m, 16H), 7.04 (t, 2H), 6.89 (t, 2H), 6.78 (d, 4H), 6.39 (d,

2

(m, 8H), 2.10 (m, 8H), 2.03 (br m, 4H), -0.06 (“t”, Pt(CH₃)₂, ²J_Pt-H

4H), 3.69 (s, 6H), 2.09 (br m, 4H), 0.47 (t, 3H, Pt(CH₃), J_Pt-H

)

) 68 Hz, J_P-H) 5.7 Hz). ¹³C{¹H} NMR (75.4 MHz, CD₃CN):

58 Hz, J_P-H) 5.7 Hz). ¹³C{¹H} NMR (125.7 MHz, CD₂Cl₂): δ

180.9 (dd, Pt(CO)), 154 (br), 136.5, 133.9 (m), 133.1, 132.9 (m),

130.8, 130.5, 128.7 (d), 128.5 (d), 126.4, 122.4, 112.6, 55.4, 18.8

(br), 17.1 (br), -2.8 (dd, Pt(CH₃)). ³¹P{¹H} NMR (121.4 MHz,

CD₂Cl₂): δ 19.89 (¹J_Pt-P) 3053 Hz, ²J_P-P) 32 Hz), 15.43 (¹J_Pt-P

) 1640 Hz, ²J_P-P) 32 Hz). ¹¹B{¹H} NMR (128.3 MHz, CD₂Cl₂):

3

δ 164 (br), 142.7 (m), 133.8 (m), 132.1, 129.4 (q), 126.0, 123.7

1

(m), 121.9, 117.5, 63.0, 22.0, 21 (br), 4.8 (dd, Pt(CH₃)₂, J_Pt-C

)

632 Hz, J_P-C) 9.3, 102 Hz). ³¹P{¹H} NMR (121.4 MHz, CD₃-

CN): δ 21.32 (¹J_Pt-P) 1848 Hz). ¹⁹F{¹H} NMR (282.1

MHz, CD₃CN): δ -63.1. ¹¹B{¹H} NMR (128.3 MHz, CD₃CN):

δ -14.2.

[[Ph₂B(CH₂PⁱPr₂)₂]Pt(Me)₂][ⁿBu₄N] (48). Following general

method C, to the resulting THF solution was added 1 equiv of

ⁿBu₄NBr. After removal of volatiles under reduced pressure, the

2

δ -14.6. IR (CH₂Cl₂): ν_CO) 2094 cm^-1

.

[(p-CF₃Ph)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (53). Following general

1

method D, 53 was generated. H NMR (300 MHz, CD₂Cl₂): δ

7.15-7.45 (m, 20H), 7.01 (d, 4H), 6.92 (d, 4H), 2.21 (br m, 4H),

2

3

0.44 (t, J_Pt-C) 58 Hz, J_P-C) 6.0 Hz). ¹³C{¹H} NMR (125.7

1

white solids were washed with Et₂O (2 × 2 mL). H NMR (300

1

2

MHz, CD₂Cl₂): δ 180.5 (dd, Pt(CO), J_Pt-C) 1288 Hz, J_P-C

)

MHz, CD₂Cl₂): δ 7.50 (br, 4H), 6.97 (t, 4H), 6.77 (t, 2H), 2.82

(m, 8H), 2.15 (m, 4H), 1.2-1.5 (m, 20H), 1.04 (m, 24H), 0.93

6.8, 132 Hz), 167 (br q), 135.9 (d), 134.0 (d), 132.9 (d), 132.3,

131.2 (d), 131.0 (d), 129.5, 128.9 (d), 128.6 (d), 125.1 (q), 123.4,

19 (br), 17 (br), -2.6 (dd, Pt(CH₃), ¹J_Pt-C) 415 Hz, ²J_P-C) 4.3,

(dd, 12H), 0.14 (t, 6H, J_Pt-H) 64 Hz, ³J_P-H) 5.1 Hz). ¹³C{¹H}

2

1

NMR (75.4 MHz, CD₂Cl₂): δ 169.2 (q, J_B-C) 50 Hz), 132.1,

61 Hz). ³¹P{¹H} NMR (121.4 MHz, CD₂Cl₂): δ 18.75 (¹J_Pt-P

)

126.4, 121.9, 59.3 (NCH₂CH₂CH₂CH₃), 24.6 (q), 24.4 (NCH₂CH₂-

CH₂CH₃), 20.3 (NCH₂CH₂CH₂CH₃), 19.8 (m), 18.8 (m), 14.0

(NCH₂CH₂CH₂CH₃), 7.9 (br), 1.2 (dd, Pt(CH₃)₂, ¹J_Pt-C) 564 Hz,

²J_P-C) 11.4, 102 Hz). ³¹P{¹H} NMR (121.4 MHz, CD₂Cl₂): δ

24.75 (¹J_Pt-P) 1961 Hz). ¹¹B{¹H} NMR (128.3 MHz, CD₂Cl₂):

δ -15.7. Anal. Calcd for C₄₄H₈₄BNP₂Pt: C, 59.05; H, 9.46; N,

1.57. Found: C, 59.10; H, 9.53; N, 1.61.

General Method D: Preparation of Bis(phosphino)borate-

Platinum Methyl Carbonyl Complexes [R₂B(CH₂PR′₂)₂]Pt(Me)-

(CO) (50-58). A solution of the bis(phosphino)borate-platinum

dimethyl anion was dissolved in THF. A THF solution containing

1 equiv of [Et₃NH][BPh₄] was added to the stirring reaction mixture.

After 15-20 min, the solution was filtered into a flask with a

sidearm, removing any solid precipitate ([X][BPh₄]). The flask was

sealed with a septum. A stream of CO gas was introduced through

the sidearm, and the flask was flushed with CO for 10 min. The

sealed flask was then stirred for an additional 60 min, after which

time volatiles were removed under reduced pressure.

2

3061 Hz, J_P-P) 31 Hz), 14.24 (¹J_Pt-P) 1631 Hz, J_P-P) 31

Hz). ¹⁹F{¹H} NMR (282.1 MHz, CD₂Cl₂): δ -62.8. ¹¹B{¹H} NMR

(128.3 MHz, CD₂Cl₂): δ -14.7. IR (CH₂Cl₂): ν_CO) 2097 cm^-1

.

[Cy₂B(CH₂PPh₂)₂]Pt(Me)(CO) (54). Following general method

1

D, 54 was generated. H NMR (300 MHz, CDCl₃): δ 7.41 (m,

8H), 7.14 (t, 8H), 6.99 (t, 4H), 2.02 (br, 2H), 1.86 (br, 2H), 1.45

(m, 8H), 1.30 (m, 8H), 0.88 (m, 4H), 0.67 (m, 2H), 0.45 (dd, 3H,

Pt(CH₃), ²J_Pt-H) 58 Hz, ³J_P-H) 6, 6 Hz). ¹³C{¹H} NMR (125.7

2

MHz, CDCl₃): δ 181.0 (dd, Pt(CO), J_P-P) 9, 130 Hz), 138.8,

138.4, 133.9 (d), 132.9 (d), 130.4 (d), 130.1 (d), 128.6 (d), 128.3

(d), 56.4 (br), 45.7 (br), 38.7 (br), 16.3 (br), 14.4 (br), -2.0 (dd,

Pt(CH₃), ¹J_Pt-C) 413 Hz, ²J_P-C) 4, 62 Hz). ³¹P{¹H} NMR (121.4

MHz, CDCl₃): δ 20.42 (¹J_Pt-P) 3037 Hz, ²J_P-P) 31 Hz), 16.23

2

(¹J_Pt-P) 1646 Hz, J_P-P) 31 Hz). ¹¹B{¹H} NMR (128.3 MHz,

CDCl₃): δ -13.3. IR (CH₂Cl₂): ν_CO) 2092 cm^-1

.

[Ph₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)(CO) (55). Following general

method D, 55 was generated. ¹³C{¹H} NMR (125.7 MHz, CD₂-

2

Cl₂): δ 180.8 (d, J_P-C) 130 Hz), δ 162.5 (br), 153.5, 153.3,

[(p-MePh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (50). Following general

1

133.3 (m), 133.2 (m), 132.3 (m), 132.2 (m), 131.9, 126.4, 125.2

method D, 50 was generated. H NMR (300 MHz, CDCl₃): δ

(d), 125.0 (d), 122.5, 34.7, 34.6, 31.2, 31.1, 18.7 (br), 16.8 (br),

7.21-7.44 (m, 20H), 6.94 (d, 4H), 6.74 (d, 4H), 2.27 (s, 6H), 2.13

1

2

2.4 (dd, Pt(CH₃), J_Pt-C) 410 Hz, J_P-C) 4.3, 62 Hz). ³¹P{¹H}

(br m, 4H), 0.57 (t, 3H, Pt(CH₃), ³J_P-H) 5.7 Hz, ²J_Pt-H) 58 Hz).

NMR (121.4 MHz, CD₂Cl₂): δ 17.48 (¹J_Pt-P) 3030 Hz, ²J_P-P

)

1

¹³C{¹H} NMR (125.7 MHz, CDCl₃): δ 180.6 (dd, Pt-CO, J_Pt-C

2

32 Hz), 12.68 (¹J_Pt-P) 1641 Hz, J_P-P) 32 Hz). ¹¹B{¹H} NMR

) 1286 Hz, ²J_Pt-P) 7.4, 131 Hz), 159 (br, ipso B(C₆H₅)₂), 136.5

(128.3 MHz, CD₂Cl₂): δ -14.7. IR (CH₂Cl₂): ν_CO) 2091 cm^-1

.

1

(d, J_P-C) 48.5 Hz), 133.5, 132.5, 132.4, 131.7, 131.4 (d, J_P-C

) 57 Hz), 130.3, 129.9, 128.3 (m), 128.1 (m), 127.5, 21.3, 18.0

[(p-MeOPh)₂B(CH₂P{p-^tBuPh}₂)₂]Pt(Me)(CO) (56). Following

general method D, 56 was generated. ¹H NMR (300 MHz,

CDCl₃): δ 7.5 (b, 4H), 7.1 (m, 8H), 6.91 (m, 4H, 6.67 (d, 4H),

6.28 (d, 4H), 3.57 (s, 6H), 1.98 (br, 2H), 1.93 (br, 2H), 1.23 (s,

2

1

(br), 16.8 (br), -2.8 (d, Pt(CH₃), J_P-C) 61 Hz, J_Pt-C) 416

Hz). ³¹P{¹H} NMR (121.4 MHz, CDCl₃): δ 20.33 (¹J_Pt-P) 3062

Hz, J_P-P) 31 Hz), 15.92 (¹J_Pt-P) 1645 Hz, J_P-P) 31 Hz).

2

¹¹B{¹H} NMR (128.3 MHz, CDCl₃): δ -13.9. IR (CH₂Cl₂): ν_CO

36H), 0.35 (dd, 3H, Pt(CH₃), J_Pt-H) 58 Hz, J_P-H) 5.7, 5.7

2

3

) 2094 cm^-1

.

Hz). ¹³C{¹H} NMR (125.7 MHz, CDCl₃): δ 180.8 (dd, Pt-CO,

²J_P-C) 130 Hz, J_Pt-C) 1278 Hz), 163.0 (q_,J_C-B) 51 Hz),

153.4, 153.1, 133.3 (m), 132.9, 132.3 (m), 128.6, 127.2, 125.2 (d),

125.0 (d), 123.3, 112.2, 55.2, 35.0, 34.9, 31.5, 31.4, 18.8 (br), 17.4

(br), -2.5 (dd, Pt(CH₃), ²J_P-C) 4.3, 62 Hz). ³¹P{¹H} NMR (121.4

MHz, CDCl₃): δ 17.65 (¹J_Pt-P) 3034 Hz, ²J_P-P) 31 Hz), 12.93

1

[(p-^tBuPh)₂B(CH₂PPh₂)₂]Pt(Me)(CO) (51). Following general

1

method D, 51 was generated. H NMR (300 MHz, CD₂Cl₂): δ

7.30 (m, 10H), 7.20 (m, 8H), 7.05 (t, 2H), 6.81 (m, 8H), 2.16 (m,

4H), 1.24 (s, 18H), 0.42 (t, 3H, Pt(CH₃), ²J_Pt-H) 58 Hz, ³J_P-H

)

6.0 Hz). ¹³C{¹H} NMR (125.7 MHz, CD₂Cl₂): δ 180.9 (dd, Pt-

(CO), ²J_P-C) 7.4, 131 Hz), 159 (br), 145.1, 136.6 (d), 136.5, 134.0

(m), 133.2 (m), 131.8, 130.8 (d), 130.5 (d), 128.6 (d), 128.4 (d),

123.7, 34.3, 32.0, 19 (br), 17 (br), -2.8 (dd, Pt(CH₃)). ³¹P{¹H}

(¹J_Pt-P) 1642 Hz, J_P-P) 31 Hz). ¹¹B{¹H} NMR (128.3 MHz,

2

CDCl₃): δ -14.8. IR (CH₂Cl₂): ν_CO) 2091 cm^-1

.

[Ph₂B(CH₂P{p-CF₃Ph}₂)₂]Pt(Me)(CO) (57). Solid [[Ph₂B-

(CH₂P(p-CF₃Ph)₂)₂]PtMe₂][ASN] and [Et₃NH][BPh₄] were dis-

solved in THF (2 mL). After 15 min, the cloudy mixture was filtered

into a J. Young NMR tube and placed under reduced pressure. An

NMR (121.4 MHz, CD₂Cl₂): δ 20.00 (¹J_Pt-P) 3044 Hz, ²J_P-P

)

2

32 Hz), 15.32 (¹J_Pt-P) 1639 Hz, J_P-P) 32 Hz). ³¹P{¹H} NMR

2

(121.4 MHz, THF): δ 20.38 (¹J_Pt-P) 3038 Hz, J_P-P) 32 Hz),

Inorganic Chemistry, Vol. 42, No. 17, 2003 5071

Thomas and Peters

Table 2. X-ray Diffraction Experimental Details for 25[Li], 25[Tl], 36[Li], 37[Li], and 38[Tl]

25[Li]

25[Tl]

36[Li]

37[Li]

38[Tl]

chem formula

fw

C₅₀H₆₅BLiN₄P₂

801.75

C₃₄H₅₈BP₂Tl

743.92

C₃₄H₅₈BLiO₂P₂

578.49

C₃₄H₆₀BLiOP₂

564.51

C₃₈H₃₄BP₂Tl

767.77

T (°C)

λ (Å)

-177

0.710 73

11.7922(6)

11.7081(6)

33.1336(18)

90

0.710 73

11.7142(9)

16.4401(13)

19.1967(15)

83.288(1)

81.391(1)

72.064(1)

3467.8(5)

P1h

0.710 73

11.3226(9)

15.4574(12)

20.5142(16)

90

0.710 73

16.295(3)

12.898(2)

17.470(3)

90

0.710 73

8.4192(6)

12.6996(9)

15.6565(11)

95.585(1)

98.293(1)

104.532(1)

1587.85(19)

P1h

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ ( deg)

V (Å³)

space group

Z

94.062(1)

90

4563.1(4)

P2₁/c

94.704(1)

90

3578.3(5)

P2₁/n

105.480(3)

90

3538.6(11)

C2/c

4

2

D

_calcd(g/cm³)

µ (cm^-1

R1,^awR2^a(I > 2σ(I))

1.167

1.33

0.0608, 0.0862

1.425

47.70

0.0370, 0.0723

1.074

1.48

0.0465, 0.0868

1.060

1.46

0.0517, 0.0896

1.606

52.13

0.0277, 0.0622

)

^aR1 ) ∑||F_o| - |F_c||/∑|F_o|, wR2 ) {∑[w(F_o- F_c)²]/∑[w(F_o)²]}^1/2

.

2

atmosphere of CO was introduced to the tube. The reaction was

heated at 55 °C for 4 h, after which ³¹P{¹H} NMR analysis verified

that the reaction had gone to completion. Volatiles were removed

under reduced pressure. Dissolution in benzene (2 mL), filtration,

and removal of volatiles under reduced pressure provided 57. H

NMR (300 MHz, CDCl₃): δ 7.51 (m, 6H), 7.39 (m, 8H), 6.81 (m,

NMR (121.4 MHz, CDCl₃): δ -29.26. Anal. Calcd for C₂₁H₂₉P:

C, 80.73; H, 9.36. Found: C, 80.53; H, 9.14.

MeP(p-CF₃Ph)₂(60). The Grignard reagent p-CF₃PhMgBr was

generated in situ from p-CF₃PhBr (16.9514 g, 75.336 mmol) and

excess magnesium turnings in Et₂O (200 mL). In a separate flask,

liquid MePCl₂(4.3978 g, 37.617 mmol) was dissolved in Et₂O (50

mL) and cooled to 0 °C. The solution of the aryl Grignard reagent

was added slowly by cannula to the cold MePCl₂solution. After

addition, the reaction was allowed to stir at rt for 2 h. The reaction

was quenched with a deoxygenated saturated aqueous solution of

[NH₄][Cl] (10 mL). The organic layer was extracted with water (3

× 30 mL) and dried over magnesium sulfate. Removal of the

volatiles by rotary evaporation provided 60 as a pale yellow solid

(8.6 g, 68%). ¹H NMR (300 MHz, CDCl₃): δ 7.63-7.60 (m, 4H),

7.56-7.50 (m, 4H), 1.71-1.69 (m, 3H). ¹³C{¹H} NMR (75.4 MHz,

CDCl₃): δ 144.4 (d), 132.5 (d), 130.9 (q), 125.4 (dq), 124.13 (q),

12.41 (d). ¹⁹F{¹H} NMR (282 MHz, CDCl₃): δ -59.89. ³¹P{¹H}

NMR (121.4 MHz, CDCl₃): δ -25.04. Anal. Calcd for C₁₅H₁₁-

F₆P: C, 53.59; H, 3.30. Found: C, 53.46; H, 3.22.

MeP(p-CF₃Ph)₂(BH₃) (61). Solid MeP(p-CF₃Ph)₂(1.5709 g,

4.6724 mmol) was dissolved in THF (1 mL). With stirring, a 2.0

M solution of BH₃‚SMe₂(2.4 mL, 4.8 mmol) was added slowly.

After 30 min, the reaction was quenched with EtOH (1 mL). The

resulting solution was concentrated under reduced pressure, provid-

ing an oil. The oil was dissolved in Et₂O (4 mL) and filtered over

a short silica plug, washing with an additional aliquot of Et₂O (2

mL). The filtered solution was concentrated under reduced pressure,

providing a pale yellow oil (1.3411 g, 82.0%). ¹H NMR (300 MHz,

CDCl₃): δ 7.70-7.85 (m, 8H), 1.96 (d, 3H, J_P-H) 10.2 Hz), 1.0

(br q, 3H, J_B-H) 95 Hz). ¹³C{¹H} NMR (125.7 MHz, CDCl₃): δ

134.6 (d), 133.7 (m), 132.5 (d), 126.1 (m), 11.6 (m). ³¹P{¹H} NMR

(121.4 MHz, CDCl₃): δ 13.11. ¹⁹F{¹H} NMR (282 MHz, CDCl₃):

δ -64.1. ¹¹B{¹H} NMR (128.3 MHz, CDCl₃): δ -39.5.

1

12H), 2.23 (m, 4H), 0.53 (t, 3H, Pt(CH₃), ²J_Pt-H) 57 Hz, ³J_P-H

)

6 Hz). ¹³C{¹H} NMR (125.7 MHz, CDCl₃): δ 179.5 (dd, Pt(CO),

²J_P-C) 7.3, 132 Hz, ¹J_Pt-C) 1296 Hz), 160 (br m), 139.7, 139.3,

133.7 (d), 132.7 (d), 131.8, 127.0, 125.5 (m), 125.2 (m), 123.4,

1

2

18.3 (br), 16.3 (br), -1.9 (dd, Pt(CH₃), J_Pt-C) 408 Hz, J_P-C

)

4.1, 61 Hz). ¹⁹F{¹H} NMR (282.1 MHz, CDCl₃): δ -64.0, -64.1.

³¹P{¹H} NMR (121.4 MHz, CDCl₃): δ 20.85 (¹J_Pt-P) 3090 Hz,

²J_P-P) 32 Hz), 16.84 (¹J_Pt-P) 1616 Hz, J_P-P) 32 Hz). ¹¹B-

2

{¹H} NMR (128.3 MHz, CDCl₃): δ -14.3. IR (CH₂Cl₂): ν_CO

)

2105 cm^-1

.

[Ph₂B(CH₂PⁱPr₂)₂]Pt(Me)(CO) (58). Following general method

1

D, 58 was generated. H NMR (300 MHz, CD₂Cl₂): δ 7.38 (br,

4H), 7.04 (t, 4H), 6.87 (t, 2H), 2.38 (d of septet, 2H), 2.17 (d of

septet, 2H), 1.53 (br m, 4H), 1.10 (dd, 12H), 1.02 (dd, 6H), 0.97

(dd, 6H), 0.79 (dd, 3H, Pt(CH₃), ²J_Pt-H) 57 Hz, ³J_P-H) 5.7, 4.8

Hz). ¹³C{¹H} NMR (125.7 MHz, CD₂Cl₂): δ 183.1 (dd, Pt(CO),

1

²J_P-C) 7, 123 Hz, J_Pt-C) 1222 Hz), 164.2 (q_,J_C-B) 50 Hz),

132.0, 127.1, 123.2, 28.9 (m), 28.7 (m), 26.0 (m), 25.7 (m), 20.3

(m), 19.9 (m), 18.8 (m), 18.7 (m), 9.0 (br), 5.5 (br), -8.6 (dd, Pt-

(CH₃), ¹J_Pt-C) 406 Hz, ²J_P-C) 6.2, 61 Hz). ³¹P{¹H} NMR (121.4

MHz, CD₂Cl₂): δ 40.28 (¹J_Pt-P) 1666 Hz, ²J_P-P) 26 Hz), 30.81

2

(¹J_Pt-P) 2942 Hz, J_P-P) 26 Hz). ¹¹B{¹H} NMR (128.3 MHz,

CD₂Cl₂): δ -14.6. IR (CH₂Cl₂): ν_CO) 2079 cm^-1

.

MeP(p-^tBuPh)₂(59). The Grignard reagent p-^tBuPhMgBr was

generated in situ from p-^tBuPhBr (19.1 g, 89.6 mmol) and excess

magnesium turnings in THF (150 mL). The mixture was cannulated

slowly over 1 h into a flask containing MePCl₂(4.97 g, 42.5 mmol)

dissolved in THF (100 mL) at 0 °C. The resultant mixture was

warmed to rt and stirred for 2 h. The reaction was quenched with

a degassed aqueous ammonium chloride solution (10 wt %, 150

mL). The organic layer was removed by a cannula under nitrogen.

The aqueous layer was extracted with dichloromethane (2 × 100

mL). The combined organic layers were dried with anhydrous

magnesium sulfate and filtered. The filtrate was concentrated under

reduced pressure, and a colorless solid was collected. Spectroscopic

General X-ray Experimental Information. Crystals of 25[Li],

25[Tl], 36[Li], 37[Li], and 38[Tl] were mounted on a glass fiber

with Paratone-N oil. Crystallographic data (Table 2) were collected

on a Bruker SMART 1000 diffractometer with a CCD area detector

under a stream of dinitrogen. Data were collected using the Bruker

SMART program, collecting ω scans at 5 φ settings. Data reduction

was performed using Bruker SAINT v6.2. Structure solution and

structure refinement were performed using SHELXS-97 (Sheldrick,

1990) and SHELXL-97 (Sheldrick, 1997).

1

data indicated it to be analytically pure 59 (11.4 g, 85.9%). H

NMR (300 MHz, CDCl₃): δ 7.35-7.30 (m, 8H), 1.59 (d, J ) 3.6

Hz, 3H), 1.30 (s, 18H). ¹³C{¹H} NMR (75.4 MHz, CDCl₃): δ

151.2, 136.5 (d), 131.8 (d), 125.2 (d), 34.6, 31.3, 12.7 (d). ³¹P{¹H}

Crystallographic data have been deposited at the CCDC, 12

Union Road, Cambridge CB2 1EZ, U.K., and copies can be

obtained on request, free of charge, by quoting the publication

5072 Inorganic Chemistry, Vol. 42, No. 17, 2003

Bis(phosphino)borates

citation and the deposition numbers 150792 (25[Li]), 203701

(25[Tl]), 203703 (36[Li]), 203700 (37[Li]), and 203702 (38[Tl]).

support from the NSF (Grant CHE-0132216), the ACS

Petroleum Research Fund, and the Dreyfus Foundation.

Supporting Information Available: CIF files and tables of

crystallographic data for complexes 25[Li], 25[Tl], 36[Li], 37[Li],

and 38[Tl], including fully labeled thermal ellipsoid plots, crystal-

lographic details, atomic coordinates, equivalent isotropic displace-

ment parameters, anisotropic displacement parameters, and inter-

atomic distances and angles. This material is available free of charge

via the Internet at http://pubs.acs.org.

Acknowledgment. The authors acknowledge Dr. Biaxin

Qian and Connie Lu for synthetic assistance. Larry Henling,

Dr. Michael Day, and Theodore Betley are acknowledged

for their assistance with X-ray crystallography. J.C.T. is

grateful to the NSF and to the Moore Foundation for graduate

research fellowships. The authors acknowledge financial

IC034150X

Inorganic Chemistry, Vol. 42, No. 17, 2003 5073

Article Doi

Bis(phosphino)borates: A new family of monoanionic chelating phosphine ligands

DOI: 10.1021/ic034150x

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic034150x

Full text of DOI:10.1021/ic034150x

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